AN OVERVIEW OF RESEARCH ACTIVITIES IN THE PHYSICS PHD … PhD... · Laboratory of spectroscopic techniques, biophysics and applied physics Prof. S. Magazù Laboratory for studying

Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina

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AN OVERVIEW OF RESEARCH ACTIVITIES IN THE PHYSICS PHD COURSE

F. Caridia,b, L. Torrisic,d

a)Facoltà di Scienze MM. FF. NN., Università di Messina, Viale F. Stagno d’Alcontres, 31 – 98166- Messina, Italy. b)INFN-Sez. CT, Gr. Coll. di Messina, Viale F. Stagno d’Alcontres, 31 – 98166- Messina, Italy.

c)Dipartimento di Fisica, Università di Messina, Viale F. Stagno d’Alcontres, 31 – 98166 – Messina, Italy. d)INFN-LNS, Via S. Sofia 44, 95124, Catania, Italy.

Abstract An overview of research activities of the PhD course

in Physics of the Messina University is reported. The research is developed mainly in the areas of matter structure, applied, theoretical and nuclear physics.

Many different laboratories are available for PhD students: laboratory of plasma physics; laboratory of acoustic and dielectric spectroscopy; laboratory of spectroscopy, biophysics and applied physics; laboratory for studying nuclear reactions on nucleons and nuclei; laboratory of IR and Raman spectroscopy; nuclear physics laboratories; laboratory of low temperature physics; laboratory of computational physics; laboratory of microanalysis, spectroscopic techniques and nanomaterials; laboratory of optical spectroscopy and laboratory of spectroscopic analyses.

A particular attention is given to collaborations of research groups and issues covered by PhD theses in recent years.

Introduction The Doctorate in Physics of the Messina University

has the aim to provide a satisfactory degree of competence and professionalism in the field of Condensed matter, Nuclear Physics, Bio-Physics and cultural heritage and environmental Applied Physics.

The research activities are developed mainly at the Physics Department and at the Matter Physics and Electronic Engineering Department of Messina University, at the National Institute of Nuclear Physics (INFN) and at the Institute for Chemical and Physical processes (IPCF) of Messina CNR.

Many other national and international collaborations also give the possibility to improve the scientific knowledge of PhD students, working in big facilities of last generation.

Research laboratories The laboratories of the PhD course are reported in

Table I.

Laboratory Responsible

Laboratory of plasma physics Prof. L. Torrisi

Laboratory of acoustic and dielectric spectroscopy

Prof. M. Cutroni

Laboratory of spectroscopic techniques, biophysics and applied physics

Prof. S. Magazù

Laboratory for studying nuclear reactions on nucleons and nuclei

Prof. G. Giardina

IR and Raman Spectroscopy Laboratory

Prof. D. Majolino

Nuclear Physics Laboratories Prof. R.C. Barnà

Laboratory of low temperature physics Prof. G. Carini

Laboratory of computational physics Prof. C. Caccamo

Laboratory of microanalysis, spectroscopic techniques and nanomaterials

Prof. F. Neri

Laboratory of optical spectroscopy Prof. G. Mondio

Laboratory of spectroscopic analyses Prof. L. Silipigni

Tab. I: Research laboratories of the PhD course

LABORATORY OF PLASMA PHYSICS Instrumentation: Laser Nd:YAG, 1064 nm e 532

nm, 3 ns, 0-300 mJ, mass quadrupole spectrometer with energy filter HIDEN EQP 300, classic mass quadrupole spectrometer BALZERS PRISMA 300, Langmuir probe, optical spectroscope, Faraday cup for time-of-flight measurements, optics and vacuum systems, detection electronics (Fig. 1).

Research activity: the experimental setup consists in a Nd:Yag laser, operating at 1064 and 532 nm, with a pulse width of 3 ns and maximum energy of 300 mJ. The beam is focalized through a optical lens at a distance of 50 cm, in order to have, in the solid target, inside a vacuum chamber, a laser spot of around 1 mm2


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at pressure of the order of 10-6 mbar. The interaction of the beam with the target produces an ablation and consequently plasma generation [1].

Applications: diagnostic of plasma laser-generated, deposition of thin films (Pulsed Laser Deposition), laser welding, nuclear physics (Laser Ion Source, D-D fusion), cultural heritage applications (compounds, isotopic ratios, surface patina analysis).

Fig. 1: Experimental setup of the Laboratory of Plasma Physics of Messina.

Collaborations: INFN-LNS, ASCR PALS Lab.,

Institute of Plasma Physics and Laser Microfusion, University of Pisa, Salento, Roma Tor Vergata and Milano-Bicocca, CELIA (Centre Lasers Intenses et Applications), MT-LAB, Bruno Kessler foundation.

LABORATORY OF ACOUSTIC AND DIELECTRIC SPECTROSCOPY

Instrumentation: setup for ultrasound analysis (MATEC TB1000 e MATEC 6000), setup for wide band measurements, wave guides.

Research activity: condensed states physics. It principally concerns problems of disorderly systems behavior. Different techniques, structural and dynamics, are employed: ultrasound (kHz-MHz), fully employed in physics and engineering for non-destroying tests (NDT), dielectric spectroscopy (systems for wide band measurements 10-3 Hz - 2 GHz), to measure the real part ε '(ω), and the imaginary part ε (ω), of the complex permittivity of a material (solid, liquid) in a wide range of frequency 10-3 Hz-2 GHz, at temperatures between 450 °K and 3 °K using only one sample. Wave guides (8.2 GHz – 40 GHz) are also employed for measurements of the complex permittivity at a frequency in the microwave range with transmission lines at rectangular wave guides and at temperatures between the room value and 10 °K [2].

Collaborations: University of Pavia, CNR–ITC, Arizona State University, Texas Tech University, Universidad Autonoma de Madrid, Chalmers University of Technology.

LABORATORY OF SPECTROSCOPIC TECHNIQUES, BIOPHYSICS AND APPLIED

PHYSICS Instrumentation: experimental setup for static and

quasi-elastic scattering measurements, infrared spectrometer for biophysics measurements.

Research activity: the laboratory disposes of top-table devices (spectroscopic techniques of elastic type, quasi-elastic and inelastic of electromagnetic radiation) useful to the dimensional and morphologic, qualitative, structural, dynamic and thermodynamic characterization of a wide class of materials of physical, biotechnological and industrial interest. The laboratory also disposes of instrumentation for measurements and analysis for ambient studies (electromagnetic pollution, air pollution, …) [3].

Applications: investigations about the mechanisms of bio-protection, micro-emulsion, gel micro-emulsion, innovative materials, physical and chemical properties of macro-molecular and polymeric systems of biological interest and optimization of physical devices for energetic and industrial fields.

Collaborations: LDSMM (CNRS), CEMHTI (CNRS), Institute Laue Langevin, Rutherford Appleton Laboratory, BENSC, ESRF, Soleil, Sanofi-Aventis, Dompè, Labplants, Cosmetic Valley, ESA, Cape Town University.

LABORATORY FOR STUDYING NUCLEAR REACTIONS ON NUCLEONS AND NUCLEI Research activity: study of barionic resonances by

mesons photoproduction at the facility ELSA in Bonn (Germany) within the international cooperation BGOOD. The Messina group in BGOOD has the tasks of experimental setup simulations (activity carried out in site) and of hardware and software administration of hydrogen and deuterium cryogenic liquid target (activity carried out in site and at ELSA).

Study of reactions induced by heavy ions for the production of superheavy elements. The experimental activity is carried out at China Institute of Atomic Energy (CIAE) in Beijing (China). Activity of calculation, experimental data analysis and interpretation is carried out in site.

Study of Bremssthralung radiation emitted during spontaneous fission processes and alpha decay of heavy elements [4].

Collaborations: Institute for Nuclear Studies, Division of Nuclear and Particle Physics, Helmholtz-Institut fuer Strahlen und Kernphysik, Institut fuer Kernphysik, Institut fur Experimentelle Kernphysik, Institute for Theoretical and Experimental Physics, Institute of Physics Jagiellonian University, Ivane Javakhishvili State University of Tbilisi, Joint Institute for Nuclear Research,

National Central University Jhongli, University of Bonn, Physikalisches Institut University of Bonn,

MQS IC

Laser

Vacuum chamber


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Helmholtz Institut f¨ur Strahlen- und Kernphysik, Petersburg Nuclear Physics Instute, University Roma Tor Vergata and INFN Roma2, INFN Roma1, INFN Laboratori Nazionali di Frascati, University of Pavia and INFN Pavia, University of Edinburgh, University of Kharkov, University of Moscow, Bogoliubov Laboratory for Theoretical Physics of JINR, Flerov Laboratory for Nuclear Reaction of JINR, Institute for Nuclear Research of NASU, Lomonosov Moscow State University.

IR AND RAMAN SPECTROSCOPY LABORATORY

Instrumentation: Interferometry Spectrometer BOMEM DA8 for IR absorption measurements in Fourier Transform (FT-IR), for measurements in Attenuate Total Reflectivity (ATR), for FT-IR micro-spectroscopy and Raman scattering measurements in Fourier Transform.

Pulverizer, hydraulic press, digital balance and electric stirrer with temperature control (50 °C – 350 °C) to prepare and store samples.

Portable XRF Analyzer ―Alpha 4000‖ Innov-Xsystems for X-Ray Fluorescence measurements (XRF).

Research activity: complete characterization of dynamic and structural and/or compositional properties of matter, both in liquid state and solid state by the use of complementary spectroscopic tecniques. Thanks to the not invasivity of the techniques, these spectroscopic methodology can surely find a large and natural application in a lot of fields nowadays fundamental [5].

Applications: archeometry, characterization, storage and recover of cultural heritage, biomedicine and/or biophysics.

Collaborations: BENSC (BErlin Neutron Scattering Center), ESRF (European Synchrotron Radiation Facility), ILL (Institut Laue-Langevin Facility), ISIS Rutherford-Appleton Laboratory Oxford, LLB (Laboratoire Lèon Brillouin).

Nuclear physics laboratories

RADIATION PROCESSING LABORATORY Instrumentation: Linac of electrons of 5 MeV

(nominal energy 5 MeV, peak current 1-200 mA, pulse time 3 sec, peak power 1 MW, power 1 kW, repetition frequency 1-300Hz, frequency RF 2.997 GHz, No. accelerating cavities 9, no magnetic lens, beam diameter 4 mm).

Applications: creation of new hydrogels, improvement of mechanic properties of UHMWPE and wood properties by impregnation and irradiation, study

of the gas diffusion in irradiated Black PE, filament winding, dejection of mycotoxins of food flour, substances released during the irradiation of different types of PE, radiative treatment of adhesive joints for structural-type applications in the aerospace and automobile field, recognizing of materials by non destructive testing techniques, calibrations to recognize irradiated foods, development of new dosimeters for radiation processing and project of accelerating systems for industries interested [6].

INFORMATICS LABORATORY Instrumentation: cluster of parallel computation (6

double-processors + file server). Protocols of Parallel Computation: PVM (Parallel Virtual Machine), MPI (Message Passing Interface).

Research activity: Monte Carlo Simulation of radiation processing treatments by MCNP-4C2 code (Monte Carlo N Particle, version 4C2) and data analysis relative to experiments carried out with the CHIMERA multidetector (LNS).

APPLIED NUCLEAR PHYSICS LABORATORY Instrumentation: lecture systems for optical

dosimeters (Gafchromic) and rivelation system of cooling Ge(Li) + spectrometer α.

Research activity: dose and dose-rate measurements, environmental radioactivity measurements (Radon measurements on samples of aspirated air on porous filters, radioactivity measurements in drinking water and on building materials).

Collaborations: INFN, Institute for Physics and Nuclear Engineering, Institute of Physics, University of Silesia, Institute of Physics, Jagellonian University, Institute de Physique Nucleaire, IN2P3-CNRS and Université Paris-Sud Orsay, LPC, ENSI Caen and Université de Caen, Saha Institute of Nuclear Physics, Kolkata, GANIL, CEA, IN2P3-CNRS Caen, Institute of Nuclear Physics Cracow, Institute of Modern Physics Lanzhou, Institute of Experimental Physics Warsaw University.

LABORATORY OF LOW TEMPERATURE PHYSICS

Experimental techniques: mechanical spectroscopy and ultrasounds; low and high temperature calorimetry; Brillouin and Raman spectroscopy; low temperature techniques; high magnetic fields; preparation of glasses and polymers.

Topics: influence of the disordered topology on the physical properties of materials; glass transition; low energy excitations; vibrational and relaxation dynamics.


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Research activity: solid state physics. Materials: glasses and polymers [7].

Collaborations: Institut für Festkörperforschung, Forschungszentrum Jülich, IPCF-CNR Messina, Institute of Macromolecular Chemistry, National Academy of Sciences of Ukraine, IMEM-CNR Parma, Institute Laue-Langevin Grenoble, Department of Chemistry and Department of Physics and Astronomy, University of Tennessee.

LABORATORY OF COMPUTATIONAL PHYSICS

Instrumentation: Parallel Cluster made of 10 PC Pentium R Dual Core E5300 @ 2.60GHz 10Gb RAM, 4Tb, at the Department of Physics; parallel cluster made of 20 knots equipped with 4 Dual Core AMD Opteron Processor 280 and 4Gb RAM for each one (ex TriGRID project), allocated at the Center for Electronic Computing ―A. Villari‖; access to grid managed by the Consorzio Cometa (http://www.consorzio.cometa.it) among the project PI2S2 (http://www.pi2s2.it).

Research activity: Statistical mechanical study of microscopic properties, structural and thermodynamic properties (including the phase equilibria) of simple and complex fluids. Integral theory of a fluid state for single site or several sites of interaction (Ornstein-Zernike equation, RISM Theory - Reference Interaction Site Model). Monte Carlo simulation methods and dynamic molecular models applied to both monatomic and molecular fluids, either pure or mixed.

Collaborations: Laboratoire de Physique des Milieux Denses, Université de Metz, France, School of Physics University of Kwazulu-Nathal, Pietermaritzburg, South Africa, CNR-IPCF Messina, University ―La Sapienza‖ Rome.

Laboratory of microanalysis, spectroscopic techniques and nanomaterials

LABORATORY OF MICROANALYSIS Instrumentation: microanalysis, imaging and depth

profiling using XPS, high yield (tens of analysis/day), visual control of positioning for the microanalysis, argon ion gun for removing surface layers, electron gun to reduce the effects of electrical charging of insulating materials, software and libraries for the automatic recognition of the chemical composition. Automated setup for measuring dc electrical conductivity as a function of temperature (100-550 °K) using the volt-amperometric method for voltage or constant current. The system is equipped with a cryostat cooled with liquid nitrogen with optical windows, to measure photoconductivity.

Measurements of profilometry and roughness on surfaces by scanning with lateral resolution of about 10 microns, and vertically up to 10 Å (Profilometer KLA-Tencor Alpha Step 500).

Research activity: physical-chemical diagnostics, morphological, structural and electrical engineering, micro- and nano-scale solid surfaces and thin film multilayer structures. By means of X-ray photoemission spectroscopy (XPS), the surface compositional mapping on the micrometer scale and the effects due to the overlapping layers of different materials are analyzed, through the depth profile analysis. The study of compositional and structural properties of thin films of SRO (Silicon Rich Oxide) and silicon oxy-nitride devices for applications in power MOSFETs and thin-film photovoltaic converters was recently approached [8].

Collaborations: ANM Research, C.S.R.A.F.A, Messina.

LABORATORY OF SPECTROSCOPIC TECHNIQUES

Instrumentation: Raman spectroscopy system. Back-scattering configuration, laser sources: multi-line Argon, diode pumped Nd:YAG (second harmonic), He-Ne. Analyzer: flat field Triax 320 monochromator coupled with a BX 40 Olympus microscope and equipped with gratings of 1800 and 600 lines / mm holographic filter to eliminate the elastic scattering component. Detector: Diode matrix CCD 1024 × 128, cooled with liquid nitrogen. Mapping micrometer with lateral resolution 1X1 (2 μm) using automated XY translation. Setup for measurements on colloidal solutions using a 10X lens focal length.

Non-linear optical spectroscopy (Z-scan technique). Measurement system in the open and closed configuration of a pulsed laser beam transmission (Nd:YAG, 5 nsec), focused by a radiometric system with two sensors and the scanning engine of the sample along the optical axis.

Research activity: physical-chemical characterization of bonding structures of materials in the form of thin films and colloidal solutions of nanoparticles: thin films of SRO (Silicon Rich Oxide), silicon-carbon alloys and carbon-based nanostructured systems, colloidal solutions of nanoparticles of metallic oxides and metallic nanoparticles for applications SERS (Surface Enhanced Raman Spectroscopy). Analysis of nonlinear optical response of colloidal systems of nanoparticles-based carbon and silicon: study of the absorption coefficient and refractive index as a function of laser pulse repetition rate, concentration and solvent.


Laboratory of nanomaterials


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Instrumentation: Nd-YAG laser pulse until the fourth harmonic (266 nm), power adjustable up to 180 mJ (second harmonic), pulse duration 5 ns, repetition up to 20 Hz, optical beam focusing, handling and control of the metal target submerged in liquid (system for laser ablation in liquids). System for spraying deposition of thin layers of colloidal solutions: the technique of spraying by automated airbrush is a methodology used for the transfer of nanoparticles in colloidal phase on surfaces of various kinds (even flexible). The system consists of a compressed gas atomizer with interchangeable nozzles of various sizes. The nozzle is placed on a medium which ensures a movement for a uniform distribution of nanoparticles on the surface to be coated. The jet is directed into a deposition chamber that houses a sample holder heated to a temperature higher than the evaporation of the solvent. A system for the removal of moisture in the deposition chamber is also provided.

Research activity: synthesis, laser ablation in liquids, and characterization of nanostructured metal oxides for the production of gas sensors and applications of metal nanoparticles for SERS (Surface Enhanced Raman Spectroscopy).


LABORATORY OF OPTICAL SPECTROSCOPY Instrumentation: PE 750 UV-Vis-Nir Perkin Elmer

(200 – 3300 nm), Lambda 2 UV-VIS-Nir Perkin-Elmer (200 – 1100 nm), FT-IR (Spectrum 100) Perkin Elmer (7800-370 cm-1) spectrophotometers; FluoroMax – 2 Jobin Ivon (200-900 nm) spectrophotofluorimeter; optical microscope.

Research activity: optical spectrophotometry (UV-VIS-NIR). Measurements of absorption of electromagnetic radiation in the UV-VIS range allow to make a qualitative analysis of a given material. The profile of an absorption spectrum depends on various parameters such as the chemical and aggregation state of the analyzed sample. In addition, the absorption at a given wavelength depends on the nature and concentration of the analyte [9].

Collaborations: ST Microelectronics, Catania, CNR Messina, RIS Messina.

LABORATORY OF SPECTROSCOPIC ANALYSES

Instrumentation: System for dielectric and electrical transport measurements (RLC HP4284A shunt, RMC LTS-LN2-VT cryostat, vacuum system (~ 10-6 torr), temperature control device Lake Shore 330, Keithley 236 unit, pc).

Research activity: study of electrical transport and dielectric properties of organic-inorganic hybrid

multifunctional materials films and powders consisting of intercalation (nanocomposite) prepared by our research group. The electronic properties of these materials are also studied, using the photoelectronic spectrometer, dual anode Mg/Al K and the optical properties by means of spectrophotometers available in the laboratory of optical spectroscopy [10].

Collaborations: IPCF-CNR Messina, CNR Napoli.

Conclusions During the last five years a number of twenty PhD in

physics were formed at the Messina University. The experience accumulated during the years of

doctoral and skills acquired allow them to aspire to scientific careers in universities, institutes of higher education, in research institutions and national (CNR, INFN, ENEA, ENI, etc..) and International Laboratories, with a special screening in Europe. The professionalism of a PhD doctor allows also the inclusion in any facility operating in areas requiring advanced professional skills through computer programming and simulation models of complex processes and teaching in secondary schools of physics, mathematics, electronic and information technology.

References [1] L. Torrisi, F. Caridi, L. Giuffrida, Nucl. Instr. And

Meth. B, 268 (2010) 2285-2291; [2] A. Mandanici; M. Cutroni, R. Rickert, Journal of

Non-Crystalline Solids, 357 (2) 264-266 (2011); [3] S. Magazù, F. Migliardo, A. Benedetto, The

Journal of Physical Chemistry B, 115 (24) 7736-7743 (2011);

[4] A.K. Nasirov, G. Mandaglio, M. Manganaro, A.I. Muminov, G. Fazio, G. Giardina, Physics Letters B, 686 (1) 72-77 (2010);

[5] G. Barone, V. Crupi, F. Longo, D. Majolino, P. Mazzoleni, V. Venuti, Journal of Molecular Structure, 993 (1-3) (2011);

[6] Auditore L., Barna R.C., Emanuele U., Loria D., Trifiro A., Trimarchi M., Nucl. Instr. and Meth. B, 266 (10) 2138-2141 (2008);

[7] G. Carini, G. Tripodo, L. Borjesson, Materials Science & Engineering A, 521-522 247-250 (2009);

[8] E. Fazio, F. Neri, S. Patanè, L. D‘Urso, G. Compagnini, Carbon, 49 (1) 306-310 (2011);

[9] A.M. Mezzasalma, G. Mondio, T. Serafino, F. Caridi, L. Torrisi, Appl. Surf. Sci., 255 (7) 4123-4128 (2009);

[10] L. Silipigni, L. Schirò, L. Monsù Scolaro, G. De Luca, G. Salvato, Appl. Surf. Sci., 257 (24) 10888-10892 (2011).


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ENHANCED OPTICAL FIELDS FOR AGGREGATION OF METAL NANOANTENNAS AND LABEL FREE HIGHLY SENSITIVE DETECTION

OF BIOMOLECULES

B. Fazioa,*, C. D‘Andreaa,b, V. Villaria, N. Micalia, O. Maragòa, G. Calogeroa and P.G. Gucciardia a) CNR – Istituto Processi Chimico-Fisici, viale F. Stagno D’Alcontres 37, 98158 Messina, Italy

* Corresponding author, e-mail: [email protected] b)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica della Materia e Ingegneria Elettronica,

viale F. Stagno D’Alcontres, 98158 S. Agata-Messina, Italy Abstract

Aggregated metal nanostructures are characterized by

strongly intense electromagnetic fields localized in the cavities region, referred as ―hot spots‖, allowing for high sensitive vibrational spectroscopy. We report on the implementation of a laser induced Surface-Enhanced Raman Scattering sensor in liquid environment by controlled aggregation of gold nanorods dispersed in solution obtained through an interplay between thermal and radiation pressure effects. The creation of highly efficient hot spot regions enables the Raman detection of proteins dissolved in buffer solution at low concentration (down to 10-7 M) with an estimated enhancement factor of 105. This methodology paves the way to a new generation lab-on-chip sensors that implies user-friendly experimental set up allowing for highly sensitive vibrational spectroscopy of biomolecules in their natural habitat and getting over the drawback of the standard methods based on the difficulty to manipulate metal nanostructures or realize active substrates that experience a highly efficient SERS.

Introduction The discovery of Surface-Enhanced Raman

Scattering (SERS) phenomena and single molecule sensitivity [1-5], due to the unique electronic and optical properties of metal nanoparticles, opened the doors to promising applications in material science and optical biosensors.

SERS from isolated metal nanostructures is usually much weaker compared to what is observed on aggregates due to the strong field enhancement occurring in the gap regions (hot spots) between adjacent nanoobjects [2-5]. A controlled creation of hot spots in liquid, the natural habitat of biomolecules, is a challenge in which optical forces play an important role. Optical trapping (OT), manipulation and deposition of metal nanostructures, gold and silver, has been at the center of an intense research [6-9].

Here we show how the simultaneous occurrence of optical, mechanical and thermal effects, promotes

aggregation of already formed gold nanorods staying in a colloidal suspension with the consequent creation of hot spot regions where biomolecules experience high field enhancement fundamental for their label free detection at submicromolar concentration. We validate the SERS biosensor efficiency by detecting biomolecules as Bovine Serum Albumin (BSA), Phenylalanine (Phe), Lysozyme (Lyz) and a protein not yet well known from a spectroscopical point of view, but of a great biomedical interest, the Manganese Superoxide Dismutase (MnSOD). Indeed, the MnSOD is considered a valid pathological biomarker, due to its levels in the plasma that are significantly higher in patients with ovarian carcinoma.

Materials and methods

Materials. Commercial gold nanorods (35x90 nm) are purchased from Nanopartz. They come in a DI water at a concentration of 0.05 mg/ml; the solution contains <0.1% ascorbic acid and <0.1% Cetyltrimethylammonium bromide (CTAB) surfactant capping preventing spontaneous re-aggregation, and have a positive -potential (+40 mV). The Bovine Serum Albumin buffered solutions at various concentrations (in the range between 10-3 M and 10-

7M) are prepared by mixing the suitable amount of BSA lyophilized powder (Sigma-Aldrich) with a 200 mM of Phosphate Buffer Solution (pH 7.2) obtained with Na2HPO4(14.94 g) and NaH2PO4 (5,063 g) dissolved in 200mL of DIwater. Then, the gold nanorods solution is added to the prepared mixture with a ratio of 1:7 v/v. An amount of 75 l of BSA and NRs solution was put inside a typical glass cell used for optical trapping experiments. Following the same procedures we prepared analogous solutions containing gold nanorods and, respectively, Lyz at 10-

6M, MnSOD at 10-4M and Phe at 10-3M in PBS. Setup. We performed the SERS experiment using a Raman Micro-Spectrometer (LabRam HR800 - Horiba Jobin Yvon) coupled to the 632.8 nm line of a He-Ne laser; the beam (P = 6.3 mW) was focused on a 500 nm diameter spot in the liquid, close to the bottom of the


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cell, by a 100X microscope objective (Olympus, NA=0.95) a droplet of the BSA and NRs solution is put inside a glass cell (a model typically used for optical trapping experiments) and placed under a Raman Micro-Spectrometer (LabRam HR800 - Horiba Jobin Yvon) coupled to the 632.8 nm line of a He-Ne laser. The spectrometer was equipped with a Peltier cooled CCD array (HJY-Synapse) as detector. The instrument was also employed to collect the extinction spectrum of the aggregate of gold NRs, by using a Xe lamp as white light source.

Figure 1: (a) Sketch of the experiment and of the

formed aggregate. (b) Absorption spectrum of the gold nanorods solution (blue line) compared to the

extinction spectrum of the photo-induced aggregate (brown line).

Results and discussion

By manually changing the fine focus inside the solution and setting it at the bottom of the cell close to the rim, the intercepted gold nanorods are mechanically constrained in a confined region; the aggregation process is activated in some seconds; in figure 1.a a sketch of the experimental configuration and the aggregate formation. Due to the slightly blue shifted excitation with respect to their LSP resonance, the gold nanorods are subjected to both a scattering force and a repulsive gradient force, so that they are not trapped in the laser focus but rather strongly pushed towards the bottom of the sample cell along the optical axis. On

the cell surface they aggregate for photoinduced thermal effect [9,10]. The extinction spectrum of the formed aggregate (figure 1,b), captured in situ, shows a broad band extinction feature, ranging between 420 and 900 nm and peaked at 770 nm, that dominates; it is suitable to underline that the 632.8 nm of laser source, used as SERS probe, falls whithin the localized surface plasmon resonance of the aggregate, while it falls outside of the single rods plasmonic absorption features (figure 1,b blue line) at λLSP = 687 nm and λLSP = 527 nm, along their long and short axes respectively [11]. The relatively high energy density (~ 25 mW/µm2) in the focal spot and the quasi resonant laser excitation of the LSPs modes causes a not negligible light absorption by the NPs which is partially converted into heat. By Stokes/Anti-Stokes Raman measurements we have estimated a temperature of about 60°C in the irradiated zone after 10 minutes of laser focusing. At this temperatures thermally induced structural rearrangement of gold nanorods in micelles capping has been observed [12]. Depolarized Light Scattering (DLS) measurements, here not shown, confirm that a thermal re-organization of the rods into small clusters takes place in the investigated solution at temperature as low as 60°C. Indeed, the mean hydrodynamic radius of about 65 nm, detected at room temperature and due to gold rods with a shell of BSA, likely stabilized by electrostatic interaction between the positively charged capping agent of the rods and the negative charge of BSA, becomes 100 nm for the gold/BSA aggregates at 60°C.

Figure 2: (a) SERS of buffered BSA molecules at 0.1 mM (black line), 1 M (red line) and 0.1 M (blue

line) . (b) Raman spectrum of buffered BSA solution at 0.1 mM without nanorods induced aggregation.

This increment of the mean size is due to thermal aggregation between gold rods mediated by BSA, that at this temperature is known to form small oligomers.


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In figure 2 is shown the strong SERS signal of BSA molecules staying in the aggregates proximity, compared to the Raman signal of the same solution in absence of aggregates formation. We estimated a SERS enhancement factor of 2x105 by the ratio between the intensity of the SERS feature of the phenylalanine ring breathing at 1004 cm-1 obtained for the buffered solution of BSA at concentration of 10-7 M and the same Raman feature collected for a buffered solution of BSA 10-3 M without gold nanorods addition. BSA at 10-3 M corresponds to the concentration limit for the Raman detection in our experiment. Under the same experimental conditions (time=10s, 4 accumulations, after a NRs aggregation time of 30s) the intensities of the SERS spectra are not depending on the BSA concentration. This occurrence confirms that what we reveal is SERS from hot spot region and suggests us that tenths of micromolar concentration of protein is not a detection limit for our experiment. However, when a concentration of 10-8 M of BSA in PBS solution is added to the same concentration of NRs solution previously used, not stable aggregates are formed and we hardly collect only SERS spectra of the CTAB surfactant. In this latter case any BSA mediation and stabilization process occurs for aggregates formation, owing to the protein negligible amount that don‘t saturate the rods quantity; as a consequence, only a transient NRs aggregation due to the optical forces is experienced and immediately disrupted by the repulsive electrostatic action of the surfactant layer. The temporal dynamics of the photothermal creation of the hot spots can be followed by acquiring consecutive SERS spectra (figure 3a) and monitoring the temporal increase of the intensity of the protein spectral signatures. We observe a preferential increment of the features attributed to the aromatic residues in the structure (Phe, Tyr, Trp), due to the intercalation of the hydrophobic side chain into the CTAB layer. The high enhancement of the 1395cm-1 COO-symmetric stretching is due to the strong electrostatic interaction with the surfactant bilayer. A similar behavior has been observed by Kaminska and coworker in the interaction between bovine pancreatic trypsin inhibitor (BPTI) and CTAB-protected gold nanoparticles deposited on functionalized silicon surface [13,14].

Figure 3: Consecutive SERS spectra of BSA in PBS solution and gold nanorods (a). Trend vs time of some protein spectral features (b).

The functionality of the SERS biosensor obtained by photoinduced aggregation of gold nanorods has been validated for many molecules of biological interest. In figure 4.a,b,c the SERS spectra of lysozyme protein, Phenylalanine amminoacid and Manganese Superoxide Dismutase, compared to the Raman signal of the respective powders are shown [15].


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Figure 4: SERS of buffered biomolecules solutions (blue lines) compared to Raman spectra of the respective powder and to the Raman spectra of the same solution in absence of gold aggregates: (a) Lysozyme in PBS at 1 M, (b) Phenylalanine in PBS at 1 mM and (c) Manganese Superoxide Dismutase at 0.1 mM.

Conclusions

In summary, we implemented a SERS biosensor based on photothermally aggregated gold nanorods, operating in liquid environment. This in situ aggregation process has been applied for the Raman detection of Bovine Serum Albumin (BSA) molecules in Phosphate Buffer Solution (PBS) at concentration down to 10-7 M. The method has been successfully validated for the SERS detection other molecules of biological interest in their natural habitat, as Phe, Lyz and MnSOD, the latter being a precious biomarker in medical diagnosis.

Acknowledgments We acknowledge funding from the EU-FP7-NANOANTENNA project GA 241818 ―Development of a high sensitive and specific nanobiosensor based on surface enhanced vibrational spectroscopy‖ and the PRIN 2008 project 2008J858Y7_004 ―Plasmonics in self-assembled nanoparticles / Surface Enhanced Raman Spectroscopy on self-assembled metallic nanoparticles.‖

References [1] M. Moskovitz, Rev. Mod.Phys. 1985, 57, 783. [2] S. Nie and S. R. Emory, Science 275 (1997) 1102. [3] K. Kneipp et al., Chemical Physics 247 (1999) 155. [4] K. Kneipp, M. Moskovits and H. Kneipp, Surface Enhanced Raman Scattering; Springer: New York, 2006. [5] E. Le Ru, P. Etchegoin, Principles of Surface Enhanced Raman Spectroscopy; Elsevier: Amsterdam, 2009. [6] F.Svedberg et al., Nano Lett., 6 (2006) 2639. [7] F. Svedberg et al., Faraday Discuss., 132 (2006) 35 [8] L. Tong, Lab Chip, 9 ( 2009) 193. [9] M. J. Guffey and N. F. Scherer, Nano Lett., 10 (2010) 4302 [10] M. J. Guffey and N. F. Scherer, Proc. of SPIE, Optical Trapping and Optical Micromanipulation VII, edited by Kishan Dholakia, Gabriel C. Spalding (2010) Vol. 7762. [11] P. H. Jones et al., ACS Nano 3 (2009) 3077. [12] M.B. Mohamed, J. Phys. Chem B., 102 (1998) 9370 [13] A. Kaminska et al., Phys Chem Chem Phys 10 (2008) 4172. [14] A. Kaminska et al., Journal Raman Spect 41 (2009) 130. [15] B. Fazio, C. D‘Andrea, V. Villari, N. Micali, O. Maragò, M.A.

Iatì, G. Calogero, P.G. Gucciardi, in preparation.


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MISSING RESONANCES AT THE BGO-OD EXPERIMENT

F. Curciarelloa,b,*, V. De Leoa,b, G. Mandaglioa,b, M. Romaniuka,b,c, G. Giardinaa,b

a)Dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy b) INFN-Sezione Catania, I-95123 ,Catania , Italy

c)Institute for Nuclear Research, National Academy of Science of Ukraine, Kiev, 03680, Ukraine *Corresponding author, e-mail: [email protected]

Abstract The excited states of nucleons are mostly treated in

the framework of the so-called ―constituent quark model‖. This model has been very successful in describing mesons and baryons into the well known multiplet structures and in the prediction of the hadronic excitation spectrum by few parameters. However there are some problems concerning the description of the observed baryon resonance spectrum by the constituent quark model. One problem is due to the so-called ―missing resonances‖: much more excited states of the nucleon are predicted by the model than the ones have been observed in experiments. It is unknown if this mismatch is caused by experimental limits or by the models used to describe the nature of quarks bonds inside nucleons. Indeed the choice of the theoretical model is of basic importance to fix the effective degrees of freedom of the constituent quarks and therefore the number of possible excited states of nucleon. For this reason other quark models have been proposed as the ―di-quark‖ model and the ―flux-tubes‖ model. The only way to establish the proper effective degrees of freedom is to test the theoretical predictions with experiment[1-2-3]. In the present paper will be presented the specific program of the BGO-OD experiment at ELSA of Bonn in the missing resonances research. The international experiment BGO-OD (INFN-MAMBO experiment) consists of a 4π-electromagnetic calorimeter, different charged sensible detectors for tracking particles, an open dipole spectrometer for charged particles and momentum reconstruction.

That experiment, thanks to the high photon luminosity (107s) of energy up to 3.2 GeV produced by electron bremsstrahlung of the ELSA cyclotron, represents a new experimental information source devoted to investigation of the ―missing resonances‖ puzzle.

Introduction The availability over the last decade of high duty-

cycle accelerators coupled with the use of large solid-angle detectors yielded a wealth of experimental information in the field of the photo- and electroproduction of mesons from the nucleons. The attempt is to extract, from photoproduction, the

electromagnetic couplings and furthermore the hadronic properties of the excited nucleon states that cannot be accessed via pion scattering, either because the resonances largely overlap, or because of a weak coupling to the single pion-nucleon channel. The energy scale which is typical of the nucleon and its resonances is the low energy regime where a perturbative approach of the QCD theory is not possible because of the strong coupling constant becomes large. This situation offers both a challenge and a chance: we do want to understand the physics laws governing the bilding blocks of the matter at low energies, in the regime where we encounter them in the nature, on the other hands is obvious that the complex many-body system ―nucleon‖ offers the ideal testing ground for concepts of the strong interaction in the non-perturbative regime. Therefore the most important step toward the understanding of the nucleon structure is the identification of the effective degrees of freedom which naturally must reflect the internal symmetries of the underlying fundamental interaction.

This step is attempted in the framework of the constituent quark model[4-5-6] which have contributed

Fig. 1 Effective degrees of freedom in quark models: three equivalent constituent quarks,

quark-diquark structure, quark and flux tubes

substantially to our understanding of the strong

interaction. The classification of the mesons and baryons in the

well known multiplet structures as derived from the symmetry, and the description of the hadronic excitation spectrum with only few fitting parameters were striking success of this model. Most of the models start from three equivalent constituent quarks in a collective potential . Here the quarks are not point-like but have electric and strong form factors. The potential is generated by a confining interaction, for example in


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the flux tubes picture, and the quarks interact via a short range residual interaction. This fine-structure interaction, usually taken as color magnetic dipole-dipole interaction mediated via one-gluon-exchange (OGE) is responsible for the spin-spin and spin-orbit terms. However, alternative models were developed. Indeed, models have been proposed that are based on a different number of degrees of freedom (see fig.1). One group of models describes the nucleon structure in term of a quark-diquark (q-q2) cluster[7], if the diquark is sufficiently strongly bound, low lying excitations of the nucleon will not include excitation of the diquark. Therefore, these models predict a fewer low-lying states of the nucleon than the conventional quark models. On the other hand other models predict an increased number of excitation states with respect the usual constituent quark model[8-9]. The choice of the theoretical model to describe nucleon structure is of crucial importance because the number of excited states with defined quantum number (baryon resonances) follows directly from the number of effective degrees of freedom of quarks inside nucleon. Consequently a comparison of the experimentally excitation spectrum to model predictions can allow us to determine the correct number of degrees of freedom and so to understand the nature of quark bonds and its interaction inside the nucleon. However, from an experimental point of view the situation is quite different from atomic and nuclear physic. The dominant decay channel of a nucleon resonance is the hadronic decay via emission of mesons (see fig. 2) . Thus, the lifetimes of the excited states are typical of the strong interaction (η~10-24s) with corresponding widths of few 100 MeV. The spacing of the resonances is often no more than a few 10 MeV so the overlap is very large, this makes difficult to identify and investigate individual states.

Fig.2 Representation of a photoproduction of meson through an intermediate state of nucleon

resonance of defined isospin I and angular momentum J.

The most widely used reactions for the study of

nucleon resonances use beams of long-lived mesons. However the exclusive use of pion induced reactions would bias the data base for resonances coupling weakly to the Nπ channel. Indeed, a comparison of excitation spectrum predicted by modern quark models to experimentally established set of nucleon resonances results in the problem of ―missing resonances‖: many

more states are predicted than have been observed. It is unknown if this evidence is related to an inept determination of effective degrees-of-freedom in the theoretical models or if it is an experimental limit. One hypothesis of this mismatch is the decoupling of many resonances from the partial wave analysis of pion scattering. This resonances can be found when other initial and/or final states are investigated. In fact, recent quark models predict a number of unobserved resonances to have large decay branching ratios for the emission of mesons other than pions. To observe this states, nucleon should be excited by scattering of respective mesons. However, most of them are short lived so the preparation of secondary beams becomes impossible. The use of induced reactions by electromagnetic interaction offers an alternative. The progress made in accelerator and detector technology during the last fifteen years has considerably enhanced our possibility to investigate the nucleon with different probes. In particular, the new generation of electron accelerators, like ELSA in Bonn, are equipped with tagged photon facilities and state-of-art detector systems.

Fig.3 Overview of the ELSA facility in Bonn which produce a photon beam up to 3.2 GeV

with the bremsstrahlung technique.

At ELSA facility the tagged high energy photon

beam is produced through the bremsstrahlung technique: electron beam from accelerator impinges on a radiator, scattered electrons produce bremsstrahlung with the typical spectral distribution 1/Eγ, with energy up to 3.2 GeV. The purpose of the experiment is to study a wide class of reactions induced by photons on nucleons and nuclei with production of pseudoscalar mesons (π0,η), pseudovettorial mesons (ω, ρ, θ) and the precise determination of the properties of baryonic resonances, in the energy region from threshold to 3.5 GeV using a polarized gamma-ray beam and/or polarized targets.


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The activities will be held in Bonn in the B1project[10] at the Physikalischen Institute of the Rheinischen Friedrich Wilhems-Universität. The involved groups and organisations are coming from Russia, Ukraine, Italy and Germany. First data taking is scheduled for the biginning of the next year.

BGO-OD experimental set-up A schematic view of the experimental apparatus

installed in the beamline S-Bonn[11] is shown in fig. 4. The experimental setup is a combination of an open-dipole forward spectrometer optimized for the detection of charged particles and of a large solid angle (25-155 degrees) detector, the BGO crystal ball, that covers the central angular region and is optimized to detect neutral particles. This particular set-up configuration is well designed to allow the investigation of photoproduction reactions and discrimination of multi-particle final states with different charges. Dipole field together with multiple tracking sections allows for momentum/charge analysis of reaction products not possible in previously experiments.

The polar angular region of small angles, θ<12°, is covered by B1 magnetic spectrometer that produces a dipolar field of about 0.5 T and that will be used for the separation, identification and reconstruction of the momentum (resolution 0.5%) of charged particles emitted in the photoproduction process . For this purpose, the spectrometer is equipped with:

a first track scintillating fibers detector (MOMO detector in fig.4) made of 672 fibers arranged on 3 layers, which allow to have a spatial resolution of 1,5 mm;

an aerogel Cĕrenkov detector for the discrimination of charged pions from protons and particulary from charged kaons in the 600-1500 MeV/c range;

a second track scintillating fibers detector (SciFi2) that consists of 640 scintillating fibers arranged in 4 circular layers;

two set of double plane drift chambers for particle tracking, placed at the exit of the dipole;

a time-of-flight detector (TOF) which provides time flight measurements for charged particles and neutrons.

The central region is covered by: the BGO, (Bi4Ge3O12), an homogeneous

electromagnetic calorimeter made of 480 truncated pyramidal crystals placed inside 24 carbon fiber baskets each one containing 20 crystals and supported by an external steel structure. Each crystal is 24 cm long (21 radiation lenghts) and provides an high energy resolution for photon detection ( ≈ 3% FWMH at 1GeV) a good response for proton with energy up to 400 MeV and a good neutron detection efficiency. The angular resolution is of about 6-8 degrees. The characteristics of the response time of the calorimeter allow to use the signal for the experimental trigger.

Each crystal is coupled to one phototube for the read out of the signals. The detector is property of INFN and used in the GRAAL experiment closed at the end of 2008;

a crystal barrel detector, made of 32 plastic scintillator bars, which allows, through measurement of ΔE, the discrimination between charged and neutral particles and, in combination with the information of energy released in the calorimeter, the identification of charged particles (protons and pions);

multi wire proportional chambers (MWPC's) for inner tracking;

multi resistive proportional chambers (MRPC's) for forward tracking;

target of H2 or deuterium that is tight enclosed by the BGO.

Fig.4 Overview of BGO-OD experimental set-up at the beam line S

Physical program The principle aim of this experiment is the

systematic investigation of the photoproduction of mesons off the nucleon. These processes are related to the structure of both, the mesons and baryons involved, whose nature of strong bonds must still be considered as poorly understood. Only such improved experiments will shed new light on the low-energy hadronic aspects of the strong interaction. Polarisation measurements are indispensable to characterize the relevant degrees of freedom in the production process of the different mesons, in particular the formation and role of the missing resonances. Therefore, meson photoproduction provides an ideal tool to investigate particular baryonic states which challenge the quark model through their unusual features. The


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photoproduction of mesons off the nucleon provides also access to several aspects of low-energy strong interaction. The mechanisms involved are not clear, in many cases not even the relevant degrees of freedom, from which resonance spectra depend. Of particular interest are the excitation and subsequent decay of baryon resonances, as well as intermediate particle exchanges in the production process, especially important in vector-meson production. To achieve one of the central goals of low-energy hadron physics, to disentangle and understand the complicated nucleon resonance spectrum, a better understanding of the meson production mechanisms is an indispensable prerequisite. It is also the basis to understand the features and hence the structure of individual states which in a striking manner do not fit to the description of quark models. Open problems are: (i) the mechanism and the relevant degrees of freedom in the photoproduction of mesons, (ii) the contrast between the general spectroscopic success of quark models and the vast discrepancy between expected and observed number of states, (iii) the structure of some well established resonances which is still not well understood.

In order to try to solve these problems, processes beyond single pion photoproduction must be investigated. Final states that involve multiple pions, η, η', K, K*, ω and θ mesons, or combinations thereof (it should be stressed that some of this mesons have masses bigger than photon beam maximum energy). It is clear that progress in this field means approaching to an understanding of the complex nature of the deepest bonds of matter known so far.

Experimentally, the new B1 magnetic spectrometer will provide high resolution and good particle identification for charged final states, in particular for K±. Since the acceptance of the spectrometer extends to almost 0-degree forward direction, it is ideally suited to investigate θ production through simultaneous K+ and K- detection. Moreover, the high resolution detection of recoil protons may not only add to our understanding of the basic production process, but also favour precision measurements regarding the in-medium properties of the ω meson. Finally, combination of the crystal calorimeter and the forward spectrometer yields a unique instrument for complicated multi-particle final states and in this way gives us access to the study of a wide range of phenomena in particle physic.

BGO CALIBRATION-EQUALIZATION In this paragraph we report an overview on the

calibration-equalization operations performed on the BGO calorimeter crystals.

We performed not a simple calibration of BGO crystals but, more important, we also made an

equalization of crystals varying high voltage applied to phototubes to homogenize their response.

The operations can be performed by remote and still continuing now in Messina.

Fig.5 Scheme of the experimental calibration chain

In fig.5 we can see a roughly representation of the

experimental chain of calibration: the output signal from the phototube, coupled to the crystal, is sent to a mixer reducing its amplitude and then reaches the ADC module for the readout. We worked on the calibration of 64 crystals at time of the 480 crystals (four ADC available for acquisition with 16 channel each one, in future with a full equipped BGO elettronics, we will have 30 ADC to acquire simultaneously signal from the 480 crystals). For the calibration we used three sources of 22Na, located inside the BGO cylindrical hole, which is characterized by two emission peaks: the first at 0.511 MeV and the second at 1.275 MeV. In order to derive the calibration constants for each channel, we tried to fix the energy of the second peak at the channel 480 of the ADCs, we also made an equalization of the crystals by changing the high voltage applied to the fototubes in order to obtain the response, (calibration peak), at the same channel of ADC for all crystals.

The calibration constant is about 0.021 MeV/ channel. The peaks have also been monitored in time and the fluctuations of the position of the second peak, due to the fitting procedure and to the response of crystal+ADC to the source, is of about 1-2 channels corresponding to about 0.021-0.042 MeV. This means an incertitude of about 1,6%-3,2% of the energy. The intrinsic resolution of the BGO+ADC at 1.275 MeV is about 25%-30%.


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Fig.6 Example of signal acquisition

BIBLIOGRAPHY

[1] A. Fantini et al. Phys. Rev. C 78, 015203(2008); [2] R. Di Salvo et al. Eur. Phys. J A 42,151 (2009); [3] G. Mandaglio et al. Phys. Rev. C 82, 045209 (2010); [4] M. Gell-Mann, Phys. Lett. 8 (1964) 214; [5] O.W. Greenberg, Phys. Rev. Mt. 13 (1964) 598; [6] R.H. Dalitz, Proceedings of the XII Int. Conf. On High Energy

Physics Berkeley, Calif. (1966); [7] M. Anselmino et al., Rev. Mod. Phys. 65 (1993) 1199; [8] R. Bijker, F. Iachello, A. Leviatan, Ann. Phys. 236 (1994) 69; [9] R. Bijker, F. Iachello, and A. Leviatan, Phys. Rev. D 55 (1997)

28; [10] http://b1.physik.uni-bonn.de/; [11] http://b1.physik.uni-bonn.de/ExperimentalSetup.


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71

RESONANT LASER ABSORPTION AND SELF-FOCUSING EFFECTS PRODUCING PROTON DRIVEN ACCELERATION FROM

HYDROGENATED STRUCTURES

M. Cutroneo1,2 and L. Torrisi1 1Dottorato di Ricerca in Fisica, Università di Messina, V.le F. Stagno D’Alcontres 31, 98166 S. Agata (ME), Italy

2Centro Siciliano di Fisica Nucleare e Strutt. della Materia, V.le A. Doria 6, 95125 Catania , Italy * Corresponding author, e-mail: [email protected]

Abstract

Resonant laser absorption and self-focusing effects were investigated as two typical non-linear processes occurring inside laser generated non-equilibrium plasmas.

The ion emission in laser-generated plasma is dealt at low and high intensities from 1010 W/cm2 up to values higher than 1016 W/cm2. The properties of plasma are strongly dependent on the time and space, laser parameters (intensity, wavelength, pulse duration, spot dimension, focal position…), target composition (polymers, metals, ceramics) and target geometry (thickness, spot/thickness ratio, surface curvature,…). A considerable interest concerns the energetic and intense proton generation for the multiplicity use that proton beams have in different scientific fields (Nuclear Physics, Astrophysics, Bio-Medicine, Microelectronics, Chemistry,…).

Measurements have been performed at INFN-LNS in Catania and at PALS Laboratory in Prague, by using low and high laser pulse intensities, respectively. Thick and thin targets and different detection techniques of ion analysis have been employed.

The mechanisms of resonant absorption of the laser light, produced in specific targets containing nanostructures with dimensions comparable with the wavelength and high electron density, enhances the proton yield and the proton kinetic energy as result of resonant absorption effects.

The mechanisms of self-focusing, obtained by changing the laser focal distance from the target surface, increase the local intensity due to further focalization the laser light in the dense vapour and consequently the plasma temperature, the density and Coulomb ion acceleration. Real-time ion detections were carried out through Thomson parabola spectrometer (TPS) coupled to a multi-channel-plate (MCP). Ion collectors (IC), SiC detectors and ion energy analyzer (IEA) have been also employed in time-of-flight configuration (TOF) technique.

The energy and the amount of protons and ions increase significantly when the two investigated non-linear phenomena occur, as it will be discussed.

Introduction

The interaction of short laser pulses with solids has become an important field of study because of many applications, such as the fast ignition scheme of inertia confinement fusion, the plasma-based particle accelerator, coherent x/ -ray sources, etc.. For most of these applications, the nature of the absorption process must be determined.

The density scale length of the plasmas generated from the target surfaces can be estimated as:

s pL c (1) where cs is the ion sound speed and p is the laser

pulse duration [1]. For high intensities (> 1016W/cm2) and very short pulses (< 1 ps)) the scale length is too short to generate sufficient absorption effects and resonance absorption at the critical surface is suggested to be one of the major absorption mechanisms. Some experiments show that it plays an important role even for plasmas with a scale length considerably shorter than the laser wavelength 0. However many theoretical works on resonance absorption are valid for the case in which L > 0 [2]. At higher laser intensity the electrons being pulled out by the ponderomotive forces and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking. Thus, the electron plasma wave is hard to develop and vacuum heating tends to be dominant [3].

A simple model is used to calculate the energy absorption efficiency when a laser of short pulse length impinges on a dielectric slab that is doped with an impurity with a resonant line at the laser frequency. It is found that the energy absorption efficiency is maximized for a certain degree of doping concentration (at a given pulse length) and also for a certain pulse length (at a given doping concentration). Absorption processes are generally dependent on the density scale length.

Interaction of the laser radiation above some threshold intensities with a plasma of defined properties may significantly increase the charge state and energy of the produced ions, due to a peculiar


72

effect occurring in the plasma, which focalizes further the laser pulse (self-focusing effect) acting so as a small vapor lens placed in front of the target surface. Advances in laser technology have recently enabled the observation of self-focusing in the interaction of intense laser pulses with plasmas. Self-focusing in plasma can occur through thermal, relativistic, and ponderomotive effects [4]. Thermal self-focusing is due to collisional heating of plasma exposed to electromagnetic radiation: the rise in temperature induces a hydrodynamic expansion, which leads to an increase of the refraction index and further heating. Relativistic self-focusing is caused by the mass increase of electrons traveling at speed approaching the speed of light, which modifies the plasma refractive index, depending on the electromagnetic and plasma frequencies. Ponderomotive self-focusing is caused by the forces which push electrons away from the region where the laser beam is more intense.

Both non-linear effects of resonant absorption and self-focusing were investigated in order to produce high yield of energetic proton emission from laser irradiated targets, as will be presented and discussed.

Experimental set-up The main experiments have been performed by using

the Nd:Yag laser of INFN-LNS in Catania and the Iodine Asterix laser of PALS Laboratory in Prague. The first has been employed at 1064 nm, 9 ns pulse duration, 800 mJ maximum pulse energy, with intensities between 108 and 1011 W/cm2. The second has been employed at 1315 nm (1 ), 300 ps pulse duration, 600 J maximum pulse energy, with intensities between 1013 and 1016 W/cm2.

In order to generate protons, the irradiated targets were thick and thin hydrogenated solids. Many of these were polyethylene based (CH2-monomer) with additions of nanostructures such as carbon-nanotubes (CNT), of length of the order of 1 micron, and oxides (such as Fe2O3). Other targets consisted of hydrogenated Si, thin films of mylar covered by Au or Al films, hydrates and metals. Generally thick films (1 mm thickness) were used at LNS for irradiation at low laser intensities to generate backward directed plasmas, while thin films (of the order of 1 micron in thickness) were employed at high laser intensity at PALS in order to generate forward directed plasmas.

Time-of-flight (TOF) measurements have been obtained with ion collectors (IC), semiconductor detectors based on SiC, and electrostatic deflector ion energy analyzer (IEA) that permits to measure the average ion energy, the ion energy and the charge state distributions, respectively. Details on IC, SiC and IEA detector are given in literature [5,6].

The ion plasma temperature, Ti, was measured though the Coulomb-Boltzmann shifted (CBS) fit of the experimental ion energy distributions given by the

IEA spectrometry [7]; the electronic plasma temperature, ne, was measured through the evaluation of the ablation yield (atoms removed from the laser crater per laser shot) and the volume of the visible plasma observed by a fast CCD camera.

A Thomson parabola spectrometer (TPS) couplet to a multi-channel plate (MCP) was also employed at PALS in forward direction along the normal to the target surface in order to separate the different ions contributions by means of magnetic deflection by using a magnetic field of the order of 0.1 Tesla and an electric deflection of 3 keV/cm. A scheme of the TPS is reported in Fig. 3b. TPS measures the energy, charge states and ion species of ejected particles from plasma for comparison with simulation programs.

Finally, a streak camera was employed at PALS to measure the laser focal position (FP) distance with respect to the target surface. Negative distances mean a focus in front of the surface while positive distances mean a focus inside the target.

Fig 1. Typical IC spectra obtained at low intensity relative to pure polyethylene irradiation (a) and

typical resonant absorption obtained by irradiating CNT nanotubes, 0.1% in concentration, embedded in

polyethylene (b).


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Results At low intensities, of the order of 1010 W/cm2 a

typical spectrum of ions emitted from polyethylene and detected by IC shows a large and slowly peak due to the carbon charge states and a faster peak due to protons, as reported in Fig. 1a.

Fig. 2: Typical proton energy distribution

relative to the ion emission from low intensity laser irradiation of pure polyethylene (a) and

relative to that from Silicon hydrogenated nanospheres target irradiated in the same

experimental conditions (b).

In this case the TOF distance is 60 cm, thus the

corresponding proton peak energy is about 75 eV. Pure polyethylene shows a low absorption coefficient to 1064 nm and a low electron density. Embedding CNT nanostructures in polyethylene the absorption coefficient changes strongly thus the result of the ion emission at low laser intensity, also, as reported in Fig. 1b. The SEM photo of the carbon nanotubes is reported in the inset of the figure. In this case the TOF length was 150 cm thus the corresponding maximum proton energy, calculated at the FWHM of the proton peak, is

about 120 eV. The comparison between the two spectra shows that the proton/carbon ratio increases from 0.05 in pure polyethylene up to 1.5 for 0.1% concentration of CNT. Thus the insertion of absorbent nanostructures, with length comparable with the laser wavelength, produces effects of resonant absorption that can be responsible of the strong increment of the proton yield emission while a negligible proton kinetic energy increment is recorded. However, significant increment of the proton energy can be obtained using other special nanostructures inducing resonant absorption effects.

At low laser intensity, a typical energy distribution of the protons emitted from an irradiated polyethylene target is reported in Fig. 2a. It gives average proton energy of about 100 eV. For comparison, the proton energy distribution obtained by irradiating amorphous surface layers of hydrogenated silicon (Si:H) with 100 nm diameter nanospheres is reported in Fig. 2b. The SEM photo of the nanospheres is reported in the inset of the figure. It gives maximum proton energy above 1.5 keV. This result may be due to a strong resonant effect generated by the high electron density of the first layers of the high absorbent target.

At high intensity, of the order of 1016 W/cm2, the produced plasma show high electron densities and the resonant absorption effects becomes more probable. A typical spectrum of ions emitted from CNT nanotubes embedded in PMMA target is provided by the Thomson Parabola spectrometer placed in forward direction along the normal to the target surface.

The comparison of the experimental parabolas (Fig. 3a) with the simulation spectra (Fig. 3c) allows us to evaluate the particle masses, energy and charge states. The spectra indicates a maximum proton energy of 1.5 MeV namely, higher value than those determined by using polyethylene targets without nanotube inserted.

The complexity of the laser interaction mechanisms with solid targets is due to the non-linearity of the processes occurring in the pre-plasma and of the plasma non linear optical properties which are dependent on the laser intensity and that occurs generally above a threshold of about 1014 W/cm2 [8]. Self-focusing effects, for example, increases the intensity of the part of laser beam on the target due to the higher focusing which may reduce the spot up to dimensions comparable with the laser wavelength. Evidence of the self-focusing occurrence may be given by IEA spectrometer of the emitted particles indicating ion energy, masses and charge states.

The plot of the ion yield versus the focal position indicates that for low charge states ions are due to ionization by thermal electrons generated by inverse bremsstrahlung mechanism. In contrast, ions with higher charge states, connected with the presence of fast electrons, and generated by resonant absorption mechanisms, create a maximum yield, kinetic energy

Yie

ld (

V)


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and charge sates when the laser focal position if placed near and in front of the target surface.

Fig. 3: Typical experimental spectrum related to Thomson Parabola placed in forward direction

with respect to the thin target with nanostructures embedded in polyethylene (a), scheme of the TPS

spectrometer (b) and comparison with the parabola simulation plot (c).

In the dense vapor generated in front of the target, in facts, the ambipolar acceleration of ions due to non linear forces, including ponderometive relativistic and self-focusing, which lead to very high laser intensity in a self-focused channel may become the main reason for the presence of high kinetic energy and high charged ions. Such a result was ascribed to the volume effect of produced plasma due to the interaction of continuously decreasing diameter of the laser beam with respect to the target surface that, in the case of self-focusing mechanisms, is found to a forward negative focus position.

Fig. 4a shows a typical example of IEA spectrum obtained by irradiating Au target in no condition of self-focusing, when the focal position is FP = + 500

m, with the focal position inside the target and high spot dimension.

In such conditions the self-focusing cannot happen because the intensity is below the threshold value and the number of charge states is only six. The inset of the figure shows a streak camera X-ray image and a scheme indicating with high precision the used focal position. Fig. 4b shows a typical example of IEA spectrum in conditions of self-focusing, when the focal position is FP = -200 m.

In such conditions the number of charge states is about 56 as result of hotter energetic plasma. Also in this case the inset of the figure shows the streak camera X-ray image and the scheme indicating the used focal position. This last effect occurs because the high light refraction effect produces a further laser beam focalization, due to the dense plasma volume in front of the target, which converges the beam so as a focusing lens.

At higher intensities the data were collected from literature and compared with our measurements in order to evaluate the generalized law of I 2 scale factor [9].

Generally a linearity of processes occurs with the law I 2, however over linear dependences occur when resonant absorption and self-focusing take place.

Discussion and conclusions The existence of an optimum laser focus position for

generation of the fastest ions with the highest charge states in front of the target surface is consistent with literature [10]. The course of dependencies and similar values of the highest Zmax indicate a threshold for the appearance of relativistic self-focusing of laser beam and a principal limitation of the maximum attainable laser intensity. At PALS differences for 1 and 3 could be ascribed to a different absorption of laser radiation, in accordance with the scaling relation I 2.

The front part of the 300 ps laser pulse interacts with the target and creates an expanding plasma plume. Considering for simplicity, the expansion velocity v =

Detector

s

z

x

-V/2

+V/2

B E

N

S

gegmD1

L12

D2

L1

Ld1

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Detector

s

z

x

-V/2

+V/2

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N

S

gegmD1

L12

D2

L1

Ld1

Ld2L2

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C5+

a) Thomson Parabola Spectrometer

C2+

C3+

C4+

H+ Ep = 1.5 MeV

b)

c)

C 5+

a)

Thomson Parabola Spectrometer C 2+

C 3+

C 4+

H+

c)

C 1 +

C6+


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106 m/s, the plasma plume attains the distance of 100 m within the first 100 ps. For the laser beam diameter

of 70 m, the self-focusing length should be about 100 to 200 m, at least. For FP = 0, the more the plasma plume expands, the longer the interaction length, but the lower the laser intensity with which the front of the plasma interacts.

Fig. 4 Typical IEA spectrum obtained at high intensity laser at PALS laboratory in Prague

relative to Au target irradiated in no self-focusing condition (a) and in self- focusing

condition (b).

The following conclusions can be made: Nano and micrometric structures, such as carbon

nanotubes, polymeric chains and molecular groups with dimensions comparable with the laser wavelength may induce resonant absorption effects increasing the plasma temperature and the acceleration ion drive mechanisms;

Resonant effects seem to be influenced by structure and composition of the target, by the plasma frequency and occur at high intensity and in the contrary of the literature also at low intensities, like we showed in this work.

Self-focusing processes influence significantly the generation of ions with the highest charge states, using high power iodine laser with the pulse length of 300 ps and an optimal FP distance can be found to enhance this effect of intensity increase due to the focal spot decreasing.

Acknowledgements Work supported by LaserLabEurope (Project No.: pals 001653) and by INFN-LIANA Project.

References [1] H. Cai, W. Yu, S. Zhu, C. Zheng, L. Cao, B. Li, Z. Y. Chen and

A. Bogerts, Physics of Plasmas 13, 094504, 2006; [2] W. L. Kruer, Physics of Laser Plasma Interactions Addison-

Wesley, New York, 1988; [3] S. C. Wilks and W. L. Kruer, IEEE J. Quantum Electron. 33,

1954, 1997; [4] L. Torrisi, D. Margarone, L. Laska, J. Krasa, A. Velyhan, M.

Pfeifer, J. Ullschmied, L. Ryc Laser and Particle Beams 26, 379-387, 2008;

[5] E. Woryna, P. Parys, J. Wolowski, and W. Mroz, Laser Part. Beams 14, 293, 1996;

[6] L. Torrisi, G. Foti, L. Giuffrida, D. Puglisi, J. Wolowski, J. Badziak, P. Parys, M. Rosinski, D. Margarone, J. Krasa, A. Velyhan and J. Ullschmied J. Appl. Phys. 105, 123304, 2009;

[7] L. Torrisi, S. Gammino,L. Andó, L. Laska, J. Krasa, K. Rohlena, and J. Ullschmied, J. Wolowski, J. Badziak, and P. Parys J. of Appl. Physics 99, 083301, 2006;

[8] L. Laska, L. Ryc, J. Badziak, F.P. Boody, S. Gammino, K. Jungwirth, J. Krasa, E. Krousky, A. Mezzasalma, P. Parys, M. Pfeifer, K. Rohlena, L. Torrisi, J. Ullschmied and J. Wolowski Rad. Eff. & Def. in Solids 160 (10–12) (2005) 557–566;

[9] L. Laska, K. Jungwirth, J. Krasa, E. Krousky, M. Pfeifer, K. Rohlena, J. Ullschmied, J. Badziak, P. Parys, J. Wolowski, S. Gammino, L. Torrisi and F.P. Boody, Laser and Particle Beams 24(1), 175-179, 2006;

[10] L. Laska, K. Jungwirth, J. Krasa, M. Pfeifer, K. Rohlena, J. Ullschmied, J. Badziak, P. Parys, L. Ryc, J. Wolowski, S. Gammino, L. Torrisi and F.P. Boody, Czech. J. of Physics 55 (6), 691-699, 2005.

NO SELF- FOCUSING

SELF- FOCUSING EFFECT

TOF ( s)

a)

b)


76


77

BARYON SPECTROSCOPY BY VECTOR MESON PHOTO-PRODUCTION AT BGO-OD EXPERIMENT

V. De Leo a,b,*, F. Curciarello a,b, G.Mandaglio a,b, M.Romanyuk a,b,c, G.Giardina a,b.

a)Dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy b)INFN- Sezione Catania, I-95123,Catania, Italy

c)Institute for Nuclear Research, National Academy of Science of Ukraine, Kiev, 03680, Ukraine * Corresponding author, e-mail: [email protected]

Abstract The study of baryon resonances plays the same role

for understanding of the nucleon structure as the nuclear spectroscopy was for the investigation on the atomic nucleus structure. Excitation energies and quantum numbers of the low lying nucleon resonances are well known. Properties like mass, spin, and parity alone , however, do not offer stringent tests of hadron models. Much more crucial tests are provided by the investigation of transitions between the states, which reflect their internal structure. The dominant decay channel of nucleon resonances is the hadronic decay via meson emission. Photo-production of mesons, which carries information on strong and electromagnetic decay properties, therefore provides a very valuable tool for their study. The progress made in the last years in accelerator and detector technologies has largely enhanced our possibilities to investigate the nucleon with different probe. The new generation of electron accelerators equipped with tagged photon facilities have opened the way to meson photo-production experiments of unprecedented sensitivity and precision. The possibilities of the starting international experiment BGO-OpenDipole (linked to the I.N.F.N. MAMBO experiment) at the ELSA facility of Bonn, which involves the hardware testing-improvement and software production contributions of the Messina group will be described in detail in the present report. The experiment represents a new sophisticate electromagnetic probe for the investigation of baryon resonances by the meson decay detections.

Introduction Current issues in the understanding of the strong

interaction address the structure of hadrons, consisting of quarks and gluons, as the building blocks of matter. Central challenges concern the questions why quarks are confined within hadrons and how hadrons are constructed from their constituents. One goal is to find the connection between the parton degrees of freedom and the low energy structure of hadrons leading to the study of the hadron excitation spectrum but the excitation spectrum of the system does not provide very sensitive tests of models [1]. The crucial tests come from the investigation of transitions between the states which are more sensitive to the model wave-

function. The dominant decay channel of nucleon resonances is the hadronic decay via meson emission to the nucleon ground state [2]. However, photon decay amplitudes are also of great interest since the photon couples only the spin flavor degrees of freedom of quarks and therefore reveals their spin-flavor correlation which are related to the configuration mixing predicted by the QCD [3]. Perturbative QCD at high energies deals with the interactions of the quarks and gluons. However, our picture of the nucleon has much more to do with effective constituent quarks and mesons that somehow subsume the complicated low energy aspects of the interaction which generate the nucleon many body structure of valence quarks, sea quarks and gluons. The most important step towards an understanding of nucleon structure is therefore the identification of the relevant low-energy effective degrees of freedom. Most nucleon models are based on three equivalent constituent quarks interacting via some QCD ―inspired‖ interaction. However, models based on quark-diquark (q – q2) configurations were also suggested and more molecular-like pentaquark ( qqq qq ) structures have been discussed in the context with certain ―nucleon‖ resonances. From the experimental point of view the main difference between nuclear and nucleon structure studies results from the large, overlapping widths of the nucleon resonances and much more important non resonant background contributions which both complicate detailed investigations of the individual resonances.

The existing data for nucleon resonances were mostly determined by πN scattering. The comparison of the set of resonances predicted by modern quark models with the set of experimentally established resonances resulted in the so-called ‘missing resonances‘ problem [4]: more resonances are predicted than observed. This problem encouraged the use of the photo-production of mesons as an alternative tool to excite the resonances. The advent of a new generation of electron accelerators allowed to perform meson photo-production experiments of unprecedented sensitivity and precision [5].

Pion scattering on a proton target has been chosen as the best tool to excite and to study the resonances of the nucleon. Nucleonic resonances are excited states of the nucleon with large mass width but with well defined spin, isospin and parity. Their identification


78

and their characterization were carried out through the analysis of the pion-nucleon scattering data by partial-wave phase-shifts method. In this method, the excitation of a given resonance is searched with the amplitude behaviour of a specific partial wave in a characteristic plot called Argand diagram [6].

The Jπ of the pseudo-scalar mesons (pions, eta, kaons) is 0−. The Jπ of the vector mesons (rho, omega) is 1−. The isospin of pions, kaons and η is 1, 1/2 and 0 respectively. The isospin is 1 for ρ and 0 for ω. All of the mesons have a short lifetime (≤ 10−7 s); however, π± and K± may have a path of several meters in the laboratory and then be detected with standard detectors similarly to stable charged particles, whereas η, η' , ρ and ω decay almost at their production point. It is worth mentioning that the rare decay modes are used as special tools to test chiral perturbation theory and basic invariance principles.

Experimental set-up. A schematic view of the experimental apparatus used

in the S-beamline of Bonn is shown in Figure 1. The Electron Stretcher Accelerator consists of three stages (injector LINAC, booster synchrotron and the stretcher ring) and provides a beam of polarized and unpolarized electrons with a tunable energy of up to 3.5 energy GeV. The bunched electron beam impinges on a radiator. Scattered electrons produce bremmstrhalungg with the tipical 1/Eγ spsectral distribution.

The polar angular region of small angles (θ < 12°) is covered by B1-magnetic field spectrometer that produces a dipolar field of about 0.5 T and that will be used for the separation, identification and reconstruction pulse resolution (0.5%) of charged particles emitted in the photo-production process.

Figure 1. Schematic view of S - beamline

accelerator ELSA in Bonn.

For this purpose, the spectrometer is equipped with: - MOMO is a scintillating fiber vertex detector with

672 channels. It consists of three layers of 224 parallel fibers (2.5mm diameter) each. The layers are rotated by 60° against each other. The arrangement yields a circularly shaped sensitive detector area of 44cm diameter. The spatial resolution is about 1.5mm, yielding effectively more than 50 000pixels. A 5cm

wide central hole allows the photon beam to pass through [7].

Figure 2. MOMO detector.

- The aerogel Čerenkov detector (ACD) that serves to reliably discriminate pions against protons, and particularly improves the K± identification substantially.

- SciFi2 detector where an active area of 66cm x 51cm is obtained using 640 scintillating fibers with a diameter of 3mm [7].

Figure 3. SciFi2 detector.

A central hole (4cm x 4cm) allows the beam to pass

through. Groups of 16 fibers are glued together to form a so-called module. The design guarantees a minimum path length (about 2mm) for particles traversing the circular fibers. The modules are arranged in two layers twisted by 90 degrees.

- Tracking of charged particles behind the spectrometer magnet is performed with eight horizontal drift chambers (DCs) which are built at the PNPI Gatchina. To cover the necessary angular range each DC has a sensitive area of at least 2456mm × 1232mm. The photon beam has to penetrate the DCs. The distance of the chambers from the target will range from 3.7 m for the first chamber up to 4.7 m for the last. For accurate positioning and simplified handling the chambers will be hanging from two support beams


79

attached to the magnet. Four of the chambers will be rotated by ± 9 degree around the beam axis. With two of the remaining chambers having horizontal wires and the other ones vertical wires four different wire orientations are obtained.

- The forward spectrometer will be complemented by a time-of-flight (TOF) detector, which is an essential component for particle identification, because it provides flight-time measurements for both, charged particles and neutrons. It has to cover the inner 10-12 degree angular range at a distance of 5m downstream of the target. It consists of four walls with a 3×3 m2 front surface, mounted on independent mechanical stands. Each wall houses 14 individual scintillating bars of 3000 mm × 200 mm × 50 mm size with photomultiplier readout at both ends.

The polar angular region between 25 and 155 degrees is covered by:

- The BGO (Bi4 Ge3 O12) Rugby Ball is a large acceptance calorimeter designed to measure multi-photon states with excellent energy resolution. The design of the calorimeter has taken into consideration a constant thickness in every direction and a central hole of radius 100 mm for the passage of the beam, target and inner detector housing. The resulting structure is made of 480 truncated pyramidal crystals of 240 mm length (corresponding to ~ 21 radiation lengths) arranged in a 15×32 matrix covering the polar angles from 25° to 155° and the whole azimuth for a total solid angle ΔΩ = 11.3 sr. The mechanical structure consists of 24 carbon fibers baskets, each containing 20 crystals, and supported by an external steel frame.

Figure 4. Overhead view of the BGO calorimeter.

The baskets are divided into cells to keep the crystals mechanically and optically separated. The thickness of the carbon is 0.38mm for the inner walls and 0.54 mm for outer walls. The steel support frame is separable into two moving halves to allow to access the central part of the detector [7].

- A cylinder of 32 plastic scintillator bars, which allows, trough the ΔE measure, the discrimination between charged and neutral particles and in combination with the energy released in the calorimeter, the identification of charged particles (protons and pions).

- The target can be a proton or deuterium target.

Hardware testing To install the BGO system in Bonn it was necessary

to replace most of electronic acquisition and HV distribution system to the crystal.

The reading of the BGO signal amplitude is made by sampling ADC modules 32 -channel multiplexer. The main characteristics of the ADC modules (AVM16 MAMBO) are the following:

-Sampling frequency 160 MHz (= 6.25ns) -12 bit resolution (corresponding to 4096 channels) -16 signal input and one trigger input. The sampling of the signal occurs within a time

interval defined by the user that can begin even before the trigger signal (in our case the time window width is 800ns). The initial samples (four) are dedicated to the determination of the baseline event subtracting automatically the value determined at the signal; the outgoing signal is thus cleaned of any background. The tests on the ADC modules were performed working with external signals and triggers, coming from a pulse generator by setting 9 different possible offset values on the baseline value. For each baseline, we have been sending a pulser signal with an amplitude varying from 100 mV to 10 mV with steps of 10 mV. The signal coming from the pulser is a wave with trapezoidal shape, time width 200 ns, rise time 5 ns, frequency 1 kHz. The procedure followed for the tests with the pulser and different baselines is the following: at first no signal is sent to the ADC and the baseline offset is set; then the baseline register is read and only at this time the signal is sent to the ADC. The value of 100 mV on the pulser current is fixed and then the baseline register is read again and the acquisition program is started; thus the acquisition program is stopped and the value of 90 mV on the pulser current is fixed. As before, the baseline register is read again and the acquisition program is started; this procedure is made for ten values of current (form 100 mV to 10 mV). The test results have highlighted some problems of the ADC modules. Strong difference was shown in the extracted value of the total integral (Qtot) with a same input signal between different modules and different channels. The response of the ADC channels to a fixed input strongly depends on the baseline offset (the response strongly increases with baseline value reaching a ―plateau‖ only for the higher baseline values). The linear behavior was checked and it was confirmed for almost all baseline offset values but the strongly dependence of the gain on the baseline offsets affects the ADC linearity. Therefore, the time synchronization features between ADC modules have been verified. The tests on ADC modules have enabled their improvement.


80

Physics The goal of this project is the systematic

investigation of the photoproduction of mesons off the nucleon. Polarization measurements are indispensable to characterize the relevant degrees of freedom in the production process of the different mesons, in particular the formation and role of hadronic resonances. The photoproduction of mesons off the nucleon provides access to several aspects of low-energy strong interaction.

The quark model predicts a large number of nucleon resonances which have not yet been observed [8]. Since the most used reaction for their study was pion-nucleon scattering, one could infer that these so-called ‗‗missing resonances‘‘ may couple weakly to this channel[9]. One possibility to investigate this issue is the photo-production of ω mesons off the proton. This channel is interesting for several reasons: first, there is no nucleon resonance well-established decaying by ω emission; second, the threshold of ω-photoproduction lies in the third resonance region, which is less explored than the first two; third, from the sparse data in the literature and a new generation experiment, evidence for resonance excitations in

γ p→ ωp is still not obvious. Due to the fact that the ω is isoscalar (I=0), the s-

channel production of this meson is only associated with the decay of N∗ (I=1/2) states and not the decay of Δ∗ (I=3/2) states, which greatly simplifies the contributing excitation spectrum. However the vector meson character of the ω implies that at least 23 observables have to be measured to disentangle all contributing resonances, instead of 8 in the pseudoscalar case. It can be hoped however, that fewer than 23 observables already provide significant constraints. In any case, the measurement of polarization observables will provide important information about the ―production mechanism‖ of the ω meson[10]. At high photon energies resonances play no role.

The cross section of vector-meson production off nucleons falls off exponentially with the squared recoil momentum, t, corresponding to the range of the mutual interaction. The t dependence of the cross section, which is approximately the same for all sufficiently high photon energies, is characteristic for ‗‗diffractive‘‘ production. It is associated with the exchange of natural parity quantum numbers (Fig. 1 left) related to the Pomeron, a composite gluonic or hadronic structure.

At large |t| deviations from pure diffraction show up. From the comparison to QCD-inspired models which are also able to describe φ and ρ0 photoproduction, the presence of hard processes in the exchange itself was thus also included at |t|>1 GeV2.

Figure 5.Contributions to ω-photoproduction: natural parity t-channel exchange (left), unnatural parity π0 t-

channel exchange (middle), s-channel intermediate resonance excitation (right).

Because of the sizeable ω→ π0γ decay (8%), significant unnatural parity π0 exchange has been expected for ω-photoproduction at smaller energies (Fig.1 middle). It was indeed observed and found dominating close to threshold. However, neither Poimeron nor π0 exchange are able to reproduce the strong threshold energy dependence of the cross section and the ω decay angular distribution observed in exclusive photoproduction and electroproducton. This was interpreted as possible evidence for s-channel contributions (Fig.1 right)[11].

Experimental support comes from a first measurement of photon-beam asymmetry, Σ , through the GRAAL collaboration[6,12]. The threshold ω-photoprodution is Eγ = 1.1 GeV; ω meson decays mainly into channels:

0

0

( . . 89%)

( . . 8.9%)

B R

B R (1)

In Bonn, the load decay channel can be observed very well by combining the BGO (π0) and the spectrometer (π + π-). Moreover, the spectrometer allows a more detailed study of other vector-meson such as the ρ-meson. Its main decay modes (to almost 100%) proceed via ρ0 → π+ π-, ρ+ → π+ π0 and ρ- → π- π0 . In particular, the last two decays that derive from the ―twins‖ reactions γ p → ρ+ n and γ n → ρ- p may be confused in case of the proton inefficiency combined with neutral noise, for this reason the BGO - spectrometer combination is crucial.

REFERENCES [1] F. Wilczek, hep-ph/0201222v2; [2] G. Mandaglio et al., Phys.RevC 82, 045209(2010); [3] R. Di Salvo et al., Eur.Phy. J A 42,151 (2009); [4] A. Fantini et al., Phys.RevC 78, 015203 (2008); [5] B. Krusche, Czech. J. Phys. 49 (1999); [6] E. Hourany, Romanian Reports in Physics, Vol. 59, No. 2, P.

457–472, 2007; [7] http://b1.physik.uni-bonn.de/ExperimentalSetup; [8] S. Capstick and W. Roberts, Prog. Part. Nucl. Phys. 45, S241

(2000); [9] J. Ajaka et al., PhysRevLett. 96, 132003 (2006); [10] A. V. Sarantsev, A. V. Anisovich, V. A. Nikonov and H.

Schmieden, Eur. Phys. J. A 39 , 61–70 (2009); [11] F. Klein, PhysRevD.78, 117101 (2008); [12] V. Vegna et al., in preparation.


81

DIODE LASERS FOR OPTICAL TRAPPING APPLICATIONS

R. Sayeda,b,*, G. Volpec, M. G. Donatob, P. G. Gucciardib, and O. M. Maragòb a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F. S. D’Alcontres 31, 98166 S. Agata-Messina, Italy

b)CNR-IPCF, Istituto per i Processi Chimico-Fisici, V.le F. S. D’Alcontres, 37, I-98158, Messina, Italy c)Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany

* Corresponding author, e-mail: [email protected]

Abstract Diode lasers can be built to meet stringent

specifications on beam stability, optical beam shape, wavelength stability, thermal stability, and compact dimensions. Stabilization of laser frequency is essential for various research fields such as metrology, frequency standards, and optical communications. Here we discuss how diode lasers can be employed in optical trapping applications, where a laser beam is tightly focused with a high numerical aperture objective at the diffraction limit to trap particles near its focal spot. In this context we will describe a novel approach to optical trapping based on optical feedback that can be applied with low numerical aperture lenses.

Keywords: Diode lasers, optical feedback, frequency stabilization, optical trapping.

Introduction Since their first use in atomic physics in the early 80's,

diode lasers have become an important part of many modern experiments [1]. This is primarily driven by the fact that they are compact, cost effective, small sized, and highly efficient [2]. For the application of diode lasers in high resolution laser spectroscopy, linewidth reduction and frequency stabilization have been actively investigated to improve the poor spectral quality of diode lasers.

In principle these systems are able to achieve high stability in their output intensity and frequency (up to 10-11). However frequency and intensity stability are considerably dependent on operational supply current and on laser diode chip temperature. Thus it is crucial to minimize fluctuations of these operational parameters. A laser diode is very sensitive to static electricity and EM interference. Its quality shielding and galvanic separation of signal wires from supply wires is not useless complication.

Our interest in diode lasers lies in their applications for novel approaches to optical trapping and laser cooling of nano and microparticles. The ability to exploit light forces for the trapping and handling of microparticles was pioneered by Ashkin [3] in the 1970‘s. Some years later the first optical tweezers (OT) was realized [4] using a laser beam strongly focused by a high numerical aperture objective lens. In these systems a particle is trapped in the

focal region of the lens by the forces arising from the scattering of light by the particle [5,6] (see Fig. 1).

Fig. 1: (left) Ray optics interpretation of optical forces on

a dielectric sphere. (a) A light-ray (red) exerts a force (dark gray) arising from its refraction and reflection. (b)

The forces on the sphere (dark gray) due to two light-rays (red and orange) compensate each-other at the

equilibrium position. (c) Restoring force on an axially displaced sphere. (d) Restoring force on a laterally

displaced sphere. (right) Exemplar 2 m latex spherical particle optically trapped in our laboratory with a diode

laser at 830nm.

Since then, OT have been extensively used for

applications in cellular and molecular biology, soft matter and nanotechnology. In biology, OT are used to make micro-mechanical experiments on cells and microorganisms both in vitro and in vivo [7-9], where the use of a near infrared wavelength (800nm-1100nm) laser prevents photodamage and thus the death of microorganisms and cells [9]. In physics, the ability to apply forces in the range of pico-Newton to micro- and nanoparticles and to measure their displacements with nanometer precision is crucial for investigation of colloidal and condensed matter systems [10]. More recently OT have been also used to manipulate, rotate and assemble a variety of nanostructures, such as carbon nanotubes [11-13], nanowires [14,15], polymer nanofibers [16], graphene flakes dispersed in water [17] and metal nanoparticles [18] and aggregates [19,20]. Here


82

we discuss a novel application of diode laser to optical trapping based on optical feedback-locking.

Theory and Overview Optical Feedback. The sensitivity of the output

intensity of a diode laser to both the amplitude and phase of external feedback is well documented [21]. The effects of optical feedback on the behavior of diode laser have shown that the dynamical properties of injection lasers are significantly affected by the external feedback, depending on the interference conditions between the laser field and the delayed field (returning from the external cavity). The essence of the optical feedback method is to increase the quality factor of the laser resonator, therefore narrowing the linewidth and stabilizing the laser's wavelength [22].

It is well known that external optical feedback strongly affects the properties of semiconductor lasers, the returned light into laser cavity causes variation in the lasing threshold, output power, linewidth, and laser spectrum. Under lasing conditions, the diode cavity is filled with gain medium, which, to a large extent, compensate for the diode cavity loss. It, therefore, has substantially greater effective quality factor, and consequently, greater influence on the laser behaviors, than the passive external cavity. For this reason, the following form of field equation has been adopted for a compound cavity laser configuration, obtained by adding an external feedback term to a standard laser equation in complex form [21], that is:

)t(iti

0Nti

e)t(kEe)t(E

)n(G21)n(ie)t(E

dtd

(1)

Here, N n is the diode cavity longitudinal mode

resonant frequency and 0 is the cavity loss of the diode

cavity, is the laser oscillation frequency, E t is the field amplitude, and is the transit time in the external cavity. The last term on the right hand side represents the external feedback and the coefficient k is related to cavity parameters as,

/ 2 Dk c l (2)

Where c is the speed of light, Dl is the cavity length of diode laser, and is refractive index of the active region. The parameter defined with the facet and external mirror reflectivities 2R and 3R as

2/1232 )R/R)(R1( (3)

It is a measure of the coupling strength between the two cavities. In the above expression for external feedback, multiple reflections in the external cavity have been neglected.

Optical Trapping. In an OT the trapping force arises from the presence of a gradient in the intensity of the optical field and tends to attract particles with refractive index higher than their surrounding towards the high-intensity regions of the field (high-field seekers), and conversely particles with lower refractive index towards the low-intensity regions (low-field seekers) [3-6]. Using simple ray diagrams it is possible to provide a very detailed picture of the physics of the trapping process, without the need for the use of involved calculus and electromagnetic theory. As can be appreciated from Fig. 1(a), when a light ray enters a transparent dielectric sphere it undergoes deflection as a result of refraction at the interfaces. Such deflection of photons that carry momentum results in a recoil force. This force (dark gray arrow in Fig. 1(a)) however does not trap the particle; it only pushes the sphere away from the light. To trap an object it is necessary to use a set of light-rays coming from different directions. If two light-rays come from opposite sides of the dielectric sphere at a very high angle they can indeed trap the particle (Fig. 1(b)). It can be easily appreciated from similar ray diagrams what happens when the sphere is displaced both axially (Fig. 1(c)) and laterally (Fig. 4(d)) with respect to the focus. In this cases the total force (black arrow) pushes the particle towards the optical trap center arises.

A simple example is a highly focused laser beam. This acts as an attractive potential well for a particle. The equilibrium position lies near – but not exactly at – the focus. When the object is displaced form this equilibrium position, it experiences an attractive force towards it. This restoring force is in first approximation proportional to the displacement; in other words, the force in the OT is well described by Hooke‘s law:

Fx= - Kx (x - x0) (4)

where x is the particle‘s position, x0 is the focus position, and kx is the optical trap spring constant along x, usually referred as trap stiffness. In fact, optical tweezers create a 3D potential well that can be approximated by three independent harmonic oscillators, one for each of the x, y, and z directions. In the xy-plane (perpendicular to the direction of the beam propagation) the force is mainly due to gradient optical forces, while along the z-direction (along the direction of the beam propagation) the restoring gradient force is weakened by the presence of radiation pressure that pushes the particle away from the focal spot. More complex intensity patterns have been obtained, for example, by interfering two or more light beams or by the use of advanced techniques such as holography and time-multiplexing.


83

Experimental Setup In our experiments, standard optical trapping is

generally achieved by focusing a 830 nm laser beam (from a laser diode Sanyo DL8142-201, 150mW nominal power) through a 100× oil immersion objective (NA=1.3) in an inverted microscope configuration (see Fig. 2 for a sketch). The laser power available at the sample is about 20mW and is kept constant during the optical force measurements. Optically trapped particles (generally latex beads with 2 m diameter) are imaged with a CCD camera (see Fig. 1).

Fig. 2: Sketch of the experimental setup and methodology for feedback-controlled optical trapping. (left) When no

particle is trapped the optical feedback on the diode laser is on and the available power at the sample permits to efficiently attract particles at the focal spot of the low

numerical aperture objective. (right) When a particle is trapped the feedback is off and the trap works at lower

power.

For the realization of feedback controlled optical

trapping we employ a low numerical aperture objective (NA=0.5). In fact, feedback controlled trapping may release the stringent requirements on numerical aperture for the operation of standard OT. In brief, in this novel configuration (see Fig. 2) the optical feedback on the diode laser source is controlled by the light scattering from a trapped particle.

When no particle is in the trap, the optical feedback from a dielectric mirror posed above the microscope objective will increase the trapping power in the focal spot. Instead, when a particle falls in the trap the optical feedback will stop and trap will work at low power preventing damage and relaxing the stringent conditions on high numerical aperture for standard OT.

Results and Discussion The resulting optical force in feedback-controlled

optical trapping is regulated by the response of the light source to the optical feedback, so it is useful to study the characteristics of diode lasers. Three diode lasers at different wavelengths and different output power have been studied.

0 20 40 60 80 100 120

0

20

40

60

80

Pow

er (

mW

)

Injected current (mA)

T= 18 OC

Ith = 33 mA

I

P

Fig. 3: L.I. curve for diode laser (Sanyo DL7140201S, 785nm, 80 mW). The measured

threshold current is Ith=33 mA.

The most important parameter of diode lasers to be

measured is the degree to which it emits light as current is injected into the device. This generates the output light versus input current known as the L.I. curve. As shown in Fig. 3 the L.I. curve for diode laser (Sanyo DL7140-201S, 785 nm, 80 mW), as the injected current is increased the laser first demonstrates spontaneous emission which increases very gradually until it begins to emit stimulated radiation, which is the onset of laser action. The exact current value at which this phenomenon takes place is typically referred to as the threshold current, Ith. It is generally desirable that the threshold current be as low as possible. It is one measure used to quantify the performance of a diode laser.

The second parameter we measured is differential external quantum efficiency of the diode laser ηD. This is defined as the ratio between the number of photons exiting the laser (∆P/hυ) to the number of electrons injected per unit time into the laser (∆I/e) and it has a typical value ranging between 0.2 and 0.7 for continuous wave lasers.

//D

P hv e Pt e hv t

(5)

where e is the electronic charge, υ is the frequency of the radiation, h is the Planck constant and ∆P/∆I is the slope efficiency of diode laser. By measuring the output power light versus current (L.I.) curve of the diode lasers Toptica photonics DL100 (403


84

30 40 50 60 700

5

10

15

20

25

30

Out

put p

ower

(m

W)

Injected Current (mA)

T1= 20 oC

T2= 29 oC

Linear Fit of T= 20 oC

TO= 85.5 K

nm, 30 mW), diode laser Nichia NDHV310ACAE1 (417 nm, 30 mW) and diode laser Sanyo DL 7140-201S (785 nm, 80 mW), the ηD is 0.28, 0.22 and 0.65 respectively. The third parameter that has been measured is the internal quantum efficiency of the diode laser ηI. It is defined as the fraction of the injected carriers that recombine radiatively and it is given by;

IP

v t (6)

where V is the power supply voltage. ηI for diode laser Toptica Photonics DL100 is 19 % , for diode laser Nichia NDHV310ACAE1, 417 nm, 30 mW, is 15 % and for diode laser Sanyo DL7140- 201S is 26 % which is calculated from slope efficiency of the experimental L. I. curve for each laser. Finally the characteristic temperature of the diode laser, To, is calculated which is defined as a measure of the temperature sensitivity of the device and dependent on the particular diode whose value is a measure of the quality of the diode. Higher values of To imply that the threshold current and external differential quantum efficiency of the device increase less rapidly with increasing temperatures. This means the laser being more thermally stable. Usually To ranges from 70 K for the worst diodes to 135 K for the best ones [23]. The ratio between the threshold values at two temperatures differing by ∆T is given by (Ith1/Ith2) = exp (∆T/To). The experimental work to determine the temperature characteristic of the GaN diode laser Toptica Photonic DL100 was made by measuring the light versus current (L.I.) curve of the lasers at various temperatures as shown in Fig. 4.

Fig. 4: L.I. curve at two different temperatures for diode laser Toptica, 403 nm, 30 mW.

From the experimental work the T0 for diode laser Toptica DL100 (403 nm) is equal to 85.5 K, T0 for diode laser

Sanyo DL 7140 201S (785 nm) is equal to 86 K and T0 for diode laser Nichia NDHV310ACAE1 (417 nm), is equal to 137 K. These results for all diode lasers showed good agreement with theoretical values. The diode laser Nichia NDHV310ACAE1 (417 nm) resulted to be the best diode laser being less sensitive to temperature changes.

Summary To summarize, diode lasers are perfectly suited for

optical trapping applications thanks to their low cost, user friendly operation, long term stability in output power and frequency. Both micro and nanoparticles (nanotubes, nanowires, graphene) are routinely trapped and manipulated in our optical tweezers experiments.

The sensitivity of diode lasers to optical feedback is the crucial enabling property for feedback-controlled optical trapping. The external optical feedback, when it is sufficiently strong, results in a large stability of the diode laser and it is much more easily detected than in other lasers because of the strong dependence of the refractive index of the diode laser active region on the carrier density. Such novel approach will open perspective for extending the use of light forces with low numerical aperture lenses much increasing the trapping depth, trapping efficiency and spatial range in experiments.

References [1] C. J. Foot, Atomic Physics, Oxford University Press, Oxford,

(2005); [2] L. Ricci, M. Weidemuller, Opt. Comm. 117(1995)541; [3] A. Ashkin, Phys. Rev. Lett. 24 (1970) 156; [4] A. Ashkin, et al. Opt. Lett. 11 (1986) 288; [5] A. Jonas, P. Zemanek, 29 (2008) 4813; [6] F. Borghese, et al. Opt. Express 15 (2007) 11984; [7] A. Ashkin, J. M. Dziedzic, T. Yamane, Nature 330 (1987) 769; [8] M. D. Wang, et al. Science 282 (1998) 902; [9] Y. Liu, et al. Biophys. J. 68 (1995) 2137; [10] D. Preece, et al. J. Opt. 13 (2011) 044022; [11] O. M. Maragò, et al. Nano Lett. 8 (2008) 3211; [12] O. M. Maragò, et al. Physica E 8 (2008) 2347; [13] P. H. Jones, et al. ACS Nano 3 (2009) 3077; [14] P. J. Pauzauskie, et al. Nat. Mater. 5 (2006) 97; [15] A. Irrera, et al. Nano Lett. (2011), DOI: 10.1021/nl202733j; [16] A. A. R. Neves, et al., Opt. Express 18 (2010) 822; [17] O. M. Maragò, et al., ACS Nano 4 (2010) 7515; [18] R. Saija R., et al. Opt. Express 17 (2009) 10231; [19] E. Messina, et al. ACS Nano 5 (2011) 905; [20] E. Messina, et al. J. Phys. Chem C115(2011) 5115; [21] C. Ye, Tunable External Cavity Diode Laser, (2004); [22] B. Tromborg, J. H. Osmundsen, IEEE J. Quantum Electr., QE-20

(1984) 1023; [23] O. Svelto, Principles of Lasers, (1993).


85

INTERFERENCE WITH COUPLED MICROCAVITIES

R. Stassia, O. Di Stefanoa, S. Savastaa a) Dipartimento di Fisica della Materia e Ingegneria Elettronica,Università di Messina Viale S. D’Alcontres, 98166

S.Agata-Messina, Italy

Abstract Here we propose an all-optical analogue of the effect of

sign change under 2π rotation based on time-resolved optical interference in coupled optical microcavities. Feeding the coupled-microcavity system with a pair of phase-locked probe pulses, separated by precise delay times, provides direct information on the sign change of the transmitted field.

Introduction In quantum mechanics if we want to perform a rotation

of a generic quantum state, we have to apply the operator U(θ) = exp(-iJ·θ/2) on the corresponding ket. A rotation by 2π radiants around the z-axis, which intuitively ought to be equivalent to no rotation at all, multiplies the eigenstate of J2 and Jz by −1 if j=n/2, with n integer, and where J is the angular momentum operator. It is necessary a rotation by 4π radians to return to its initial state. As observables in quantum theory are quadratic in a wave function, the change of sign cannot be detected by ordinary experiments.

The first Gedanken experiments aimed at the observation of the sign change of spinors under 2π rotations were published by Bernstein and independently by Aharonov and Susskind. These two proposed experiments, the first involving the interaction of a spin 1/2 particle with a magnetic field, and the second involving the tunneling of a current of free electrons, were conceptually similar. In both cases one system was split into two separate subsystems, one of them was affected by an additional 2π rotation relative to the other one, and then recombined. The first experimental verification of coherent spinor rotation was provided by Rauch et al. and Werner et al., both groups employed unpolarized neutron interferometry as suggested in the Bernstein-Gedanken experiment. Klein and Opat reported the observation of 2π rotations by neutron Fresnel diffraction. The similarity of the mathematical description (that is, the algebraic isomorphism) between spinor rotations and the transitions between two atomic or molecular states of any total angular momentum has been exploited to study analogies of 2π spin rotations with different experimental approaches that required no fermions. One other system, where such an effect has been observed, consists of strongly interacting Rydberg atoms and microwave photons: after a full cycle of Rabi oscillation, the atom-cavity system experiences a global quantum phase shift π.

We consider a system of two coupled planar microcavities (MCs). When one of the two is excited by an ultrafast resonant optical pulse, the energy oscillates between the two systems until losses through the external mirrors prevail. In such systems the coupling of the two cavity modes can be controlled by the transmission of the central mirror and the two resonant modes are the optical analogs of two atomic or molecular states, which, in turn, are isomorphic to a spin 1/2 system. We provide with this system a concrete and conceptually simple all-optical realization of the sign change under 2π rotations.

Two Coupled Oscillators with source term A semiconductor planar MC is a structure formed by

high reflecting dielectric mirrors [distributed Bragg reflectors (DBR)] on the two sides of a spacer (Sp) layer, of physical length LC.

Here, we consider a system composed by two planar MCs connected through a common DBR (see Fig. 1). We assume that the two MCs have a high Q factor and that the intracavity modes are coupled with the external field via two partially transmitting mirrors. In the figure 2, the dashed line represents the single mode of an empty microcavity. The continuous line represents the splitting in energy of the former mode when we couple two identical microcavities. The two resonant modes are the optical analogues of two atomic or molecular states, which, in turn, are isomorphic to a spin 1/2 system. We consider systems with coupling-induced splitting quite larger than the linewidth of the individual peaks.

Figure 1: Scheme of a double microcavity


86

Figure 2: Resonant modes of (dashed line) one empty MC and (continuous line) two coupled

MCs.

We consider excitation of the system by a Gaussian

light pulse arriving from the left of the coupled system

2

20

00 2)tt(

)tt(1 ee

21)t( (1)

The calculated field intensity is shown Fig. 3. The

figure also displays (arb. units) the corresponding Gaussian input pulse. The transmitted intensity displays a damped oscillatory time behavior (with Rabi frequency ΩR) originating from the combination of coherent energy exchange between the two MCs and losses through the external mirrors. To inspect the phase of the transmitted field after one or two Rabi-like oscillations, we now consider a second pulse in phase with the first one sent from the left into the double semiconductor planar MCs. The total input field can be expressed as,

2

21

10 2)tt(

)tt(12 ee

21)t()t( (2)

The transmitted intensity is calculated for two different

physical situations as shown in Fig. 4 and 5. First we address the case when the arrival time of the second pulse is chosen so that the corresponding first maximum in the transmitted field is exactly in time with the second maximum originating from the first pulse Fig. 4. In particular the time delay between the two pulses corresponds to a complete Rabi-like oscillation: ΩR(t1-t0)=2π. In this case we find that the total signal is strongly damped due to destructive interference.

Figure 3: light field transmitted intensity inside the cavity in function of time when is sent a single

excitation.

Figure 4: transmitted intensity calculated when a second pulse is sent after one complete Rabi-like

oscillation.

Figure 5: transmitted intensity calculated when a second pulse is sent after two complete Rabi-like

oscillations.


87

Hence, such an abrupt damping of the signal

demonstrates that the transmitted field after a complete oscillation acquires a π phase (minus sign). If the arrival time of the second pulse is chosen so that ΩR(t1-t0)=4π (see Fig. 5) the total signal gets amplified due to constructive interference. This condition is verified when the corresponding first maximum in the transmitted field is exactly in time with the next (third) maximum originating from the first pulse.

Analytical Model The essential physical features of such a system may be

understood through a simplified analytical model. We adopt the quasimode approach. The discrete cavity modes (one for each MC) interact with an external multimode field. The quasimode approximation allows us to describe such systems analogously to a two interacting oscillators system. In particular, we consider a system of two coupled harmonic oscillators (the light modes of the two coupled cavities) with an external source ε(t). The Hamiltonian of such a system can be written as

† † † †0 0

† *

( )

( ) ( )

H a a b b g a b b a

t a t a (3)

where a and b are, respectively, the bosonic operators

relative to the single mode in each cavity, the coupling g depends on the reflectivity of the central mirror, and ε(t) describes the feeding of the cavity by a classical input beam. The resulting evolution equations for the photon operators inside the two cavities are

0

0

( )2

2

d ii a a g b a tdtd ii b b g a bdt

(4)

where <・> indicates the mean value of the operator,

and γ takes into account the damping and losses of a field inside the structure and may be considered as a phenomenological parameter or as obtained from the master equation for two coupled oscillators interacting with a zero-temperature thermal reservoir. In the rotating frame (putting ω0 = 0), if losses are neglected (γ = 0) and considering the input field in the cavity as a sharp pulse sent at t = t0 we obtain

0

0

0† 22

0† 22

( )cos2

( )sin2

1 cos ( )2

1 cos ( )2

R

R

R

R

t tAa i

t tAb

t ta a A

t tb b A

(5)

where ΩR = 2g/ħ represents the Rabi frequency. We

now calculate the number of photons emerging from the cavity on the right, <b†b>, that can be measured by a photodetector. Inspecting the last two equations, we observe that it oscillates with a Rabi of frequency ΩR. Instead, we observe, as is evident from the first two equations, that b oscillates with a double period with respect to the light cavity population (i.e., at a frequency equal to ΩR/2). After a Rabi period T = 2π/ ΩR, we have <b>T = −<b>0 = -A/ħ. Such behavior is the optical analog of the spin-1/2 system undergoing a 2π rotation in ordinary space. In addition, if the time delay is t = 2T = 4π/R (i.e., after a 4π Rabi oscillation) then <b>T = −<b>0 = A/ħ: the two signals are now in phase and we have the corresponding 4π rotation in a spin-1/2 system. We observe no phase change behavior in <b†b>. The results in this section show that the simple analytical model here analyzed contains all the essential physics of the process including the π phase shift after a complete Rabi-like oscillation.

Conclusion In this paper we proposed an all-optical analog of the

well-known sign change of the spinor wave functions under 2π rotations. The system here investigated consists of two planar MCs coupled through a central mirror. Here the two modes (in the absence of coupling) play the role of the two spin states, whereas the coupling induces a quasiperiodic exchange of the optical excitation among the two modes after ultrafast optical excitation. A complete oscillation of the excitation from one mode to the other and back is the optical analog of a 2π spin rotation. We showed that by feeding the coupled-MC system with a pair of phase-locked probe pulses separated by precise delay times, we can gather direct information on the sign change of the transmitted field after one complete Rabi-like oscillation period. Such results were explained qualitatively by a simplified physical model considering two coupled damped oscillators


88

References [1] H. J. Bernstein, Phys. Rev. Lett. 18, 1102 (1967); [2] Y. Aharonov and L. Susskind, Phys. Rev. 158, 1237 (1967); [3] H. Rauch, A. Zeilinger, G. Badurek, A.Wilfing,W. Bauspiess, and

U. Bonse, Phys. Lett. A 54, 425 (1975); [4] S. A.Werner, R. Colella, A.W. Overhauser, and C. F. Eagen,

Phys.Rev. Lett. 35, 1053 (1975); [5] A. G. Klein and G. I. Opat, Phys. Rev. D 11, 523 (1975); Phys.

Rev.Lett. 37, 238 (1976); [6] A. Abragam, The Principles of Nuclear Magnetism (Clarendon

Press, Oxford, 1961); [7] E. Klempt, Phys. Rev. D 13, 3125 (1976); [8] M. P. Silverman, Eur. J. Phys. 1, 116 (1980); [9] J. M. Raimond, M. Brune, and S. Haroche, Rev. Mod. Phys. 73, 3

(2001);

[10] A. Ridolfo, S. Stelitano, S. Patané, S. Savasta, and R. Girlanda, Phys. Rev. B 81, 075313 (2010);

[11] M. E. Stoll, A. J. Vega, and R. W. Vaughan, Phys. Rev. A 16, 1521 (1977);

[12] A. Armitage, M. S. Skolnick, V. N. Astratov, D. M. Whittaker, G Panzarini, L. C. Andreani, T. A. Fischer, J. S. Roberts, A. V. Kavokin, M. A. Kaliteevski, and M. R. Vladimirova, Phys. Rev. B 57, 14877 (1998);

[13] G. Panzarini, L. C. Andreani, A. Armitage, D. Baxter, M. S.Skolnick, V. N. Astratov, J. S. Roberts, A. V. Kavokin, M. R.Vladimirova, and M. A. Kaliteevski, Phys. Rev. B 59, 5082 (1999);

[14] S. Vignolini, F. Intonti, M. Zani, F. Riboli, D. S.Wiersma, L. Balet, L. H. Li, M. Francardi, A. Gerardino, A. Fiore, and M. Gurioli, Appl. Phys. Lett. 94, 151103 (2009);

[15] 28P. Yeh, Amnon Yariv, and Chi-Shain Hong, J. Opt. Soc. Am. 67, 423 (1977).


89

SPECTRAL DEPENDENCE OF THE AMPLIFICATION FACTOR IN SURFACE ENHANCED RAMAN SCATTERING

C. D‘Andreaa,b,*, B. Fazioa, A. Irreraa, P. Artonic, O.M. Maragòa,

G. Calogeroa and P.G. Gucciardia a) CNR – Istituto Processi Chimico-Fisici, Viale F. Stagno D’Alcontres, 37, I-98158, Messina, Italy

b) Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F. S. D’Alcontres, I-98158 S. Agata - Messina, Italy c) MATIS, CNR - Istituto per la Microelettronica e i Microsistemi, Via S. Sofia, 64, I-95123, Catania, Italy


Abstract Surface Enhanced Raman Scattering (SERS) is

characterized by a strong signal amplification (up to 108÷10) when both the excitation and the Raman photons frequencies match the localized plasmon resonances (LSPR) of the nanoparticles (NPs). In order to understand if the effective LSPR profile refers to the bare NPs or to the resonance of NPs ―dressed‖ with the probe molecules, we perform multiwavelength (514nm, 633nm and 785nm) SERS experiments using evaporate gold NPs as SERS-active substrate on which we deposited Methylene Blue molecules (MB) that yields a resonance energy red-shift and a broadening of the LSPR profile.

The SERS spectra at the investigated excitation wavelengths display a different intensity ratio of the characteristic MB band (peaks at 450 cm-1 and 1620 cm-1) with respect to the Raman counterpart.

In presence of MB molecules, a red shift of 50 nm in the LSPR is observed

The enhancement of the Raman modes at the different excitation wavelengths follows a trend similar to the LSPR profile of the ―dressed‖ NPs, although the maximum enhancement is found at 785nm excitation, in spite of a LSPR peak at 600nm.

Introduction Surface enhanced Raman Scattering (SERS) is an

ultrasensitive spectroscopy technique that allows the detection of molecules adsorbed on noble metal nanoparticles (Au, Ag, Cu, etc) at sub-pico molar concentrations and enables to detect, under optimal condition, a single molecule [1, 2].

The giant signal amplification of SERS is related to the collective excitation of nanoparticles (NPs) conduction electrons, the so-called localized surface plasmon resonance (LSPR). When the frequency of incident photons is resonant with the LSPR of NPs, an increase of the electromagnetic (EM) fields can be obtained in the region close to the NPs surface, called Hot spots [3]. In particular, in SERS, when both the excitation and the Raman photons frequencies (ωL and ωR, respectively) are resonant with the LSPR of the NPs, the enhancement can reach 108÷10 order of magnitude as demonstrated

experimentally [4-8] and theoretically, according to the |E|4 approximation [9,10].

The LSPR profile strictly depends on the size/shape of the particles, the inter-particle distance, the surrounding medium [11,12], and the spectral dependence of both the excitation field enhancement factor Aexc(ω) and the re-radiation enhancement factor Arad(ω) have been observed to be proportional to the LSPR profile, Q(ω) [4, 12]. The spectral dependence of Q(ω) is therefore particularly important since it determines both the best excitation wavelength for optimal SERS detection and the re-radiation enhancement of the Raman modes.

It is still not known, however, whether the effective Q(ω) refers to the LSPR of the bare NPs or to the resonance of the NPs ―dressed‖ with the probe molecules [Qdress(ω)]. The latter is typically energy shifted and can be much broader, according to the molecular dielectric constant.

The LSPR profiles can be obtained easily by extinction spectroscopy, which is the easiest and most powerful tool to study the resonance energy of metal NPs. Differently from the extinction spectroscopy that is a far-field technique, SERS measurements give insight on the ―local‖ near-field (the field in the hot spots) so, detailed comparison of the SERS enhancement factor (EF) with the LSPR profiles of SERS-active substrates is a possible way to understand the properties of the electromagnetic hot spots in NPs.

To get insight on this phenomenon we carried out multi-wavelength SERS experiments using evaporated gold nanoparticles as SERS-active substrates on which we deposited Methylene Blue molecules that notably alter the LSPR profile. The SERS peaks intensities, normalized to the Raman intensities measured on a flat gold region, and the relative enhancement factor of the Methylene Blue Raman modes were compared with the LSPR spectra highlighting an additional frequency shift, not appreciable in the LSPR profile.

Materials and methods The gold clusters were prepared by Electron Beam

Evaporation (EBE) on SiO2.The sample was heated at 480°C and a gold amount of 1 1016 cm-2 was evaporated.


90

Figure 3: Extinction spectra of bare Gold Nanoparticles (black line) and after (blue line) the

binding of the Methylene Blue molecules. The three colour line and box indicate the excitation line and the corresponding Raman region of MB

for the three lasers of our apparatus.

Gold atoms arrive on the heated substrate, so they have

the possibility to diffuse over the substrate, immediately starting a ripening process leading to cluster formation. In order to promote the adhesion of the gold NPs to the substrate, the clusters were covered by a thin Silicon Oxide layer (2-3 nm) produced by RF magnetron sputtering.

The Methylene Blue (MB) solution was prepared mixing deionized water with the powder (Carlo Erba Reagenti) at the concentration of 10-4 M. The samples of gold NPs were soaked into aqueous solution of dye for 1h, then washed in water and dried in vertical position to avoid formation of too thick multilayer of molecules on substrates. This method guarantees that only a single layer of MB dye remains adsorbed onto the array, as reported in literature [3,7,13]. Extinction and SERS experiments were carried out with a HR800 – Jobin Yvon micro-spectrometer. For the extinction measurements, we exploiting the white light xenon lamp embedded in the microscope of the HR800 spectrometer. A 10X objective was used to collect the light transmitted through the sample and the HR spectrometer was used to acquire the optical signal. The LSPR profile was then proportional to the ratio between the light transmitted in absence (I0) or in presence of NPs (INPs). For multi-wavelength SERS measurements we coupled our spectrometer with an Ar++ (515 nm), a He-Ne (633 nm) and a diode (785 nm) laser. In this back-scattering Raman setup, measurements were done focusing a few tens of µW of laser power on a submicron spot using a 100X microscope objective (NA 0.95). All the spectra were acquired with integration times from 10 to 120 seconds and power over the range from 4 to 400μW.

Discussion Figure 1 shows the different LSPR profiles between the

bare NPs (blue line) and ―dressed‖ NPs (black line). The presence of a layer of Methylene Blue molecules bound to the gold NPs substrate yields a resonance energy red-shift of about 50 nm (from 570 nm to 620 nm) and a broadening of 50 nm. By using the several excitation wavelengths available in the experimental set up, we were able to excite the ascending and the descending region of the dressed LSPR profile Qdress(ω) (with 515 nm and 633 nm laser lines), and the out of resonance region (by using the laser line at 785nm), where we don‘t expect SERS effect (colour lines in Fig. 1). As shown in figure 1 by the colour boxes relative to each excitation wavelength, the Raman spectrum of MB extends in the 400 – 1650 cm-1 region [7, 13] with the most intense peaks at 450 cm-1 and 1620 cm-1.

According to previous study [14], looking the extinction profile, for the laser excitation at 515 nm we can expect a progressive increase of the intensity of the SERS Raman mode of MB passing from the low frequencies to the higher, with respect to the Raman mode in absence of SERS effect. An opposite behaviour is envisaged for the laser excitation at 633 nm; in this condition the 450 cm-1 bands are closer to the LSPR peak, and then to the condition of maximum resonance.

The SERS spectra at the investigated excitation wavelengths (fig. 2, colour lines) display, as expected, a different intensity ratio of the 450 cm-1 and 1620 cm-1 peaks with respect to the Raman counterpart. For each excitation wavelength, in fact, to comparing SERS and Raman spectra and to calculate the EF, we acquired the MB Raman modes coming from a flat gold region (fig 2, black lines). This expedient allowed us, also, to exclude any contributions linked to chemical bonds between gold and Methylene blue.

Figure 4: SERS spectra of Methylene blue for 515, 633 and 785 nm excitation wavelength (colour

line) compared with the Raman counterpart acquired on a flat gold region (black line).


91

At 515 nm (green line) the 1620 cm-1 mode is more enhanced with respect to the peak at 450 cm-1, but a similar trend is also observed for excitation wavelength at 633 nm (red line). This behaviour is not compatible with the both the LSPR profiles acquired in the extinction measurements. This trend is extended until the near infrared region by using an excitation wavelength of 785 nm; here the SERS spectra show a higher enhancement of the modes at 450 cm-1 than those at 1620 cm-1.

Comparing the intensity of the principal bands of Methylene Blue SERS spectra with the corresponding Raman modes, it was possible to plot the relative mode enhancement factor versus the Raman shift for each excitation wavelength, as showed in figure 3. In this picture is evident the incremental behaviour of the EF for the visible excitations: at 515 nm we have an enhancement from 8 times for the low frequency modes, to 30 for the bands at 1620cm-1. In the same way, at 633 nm (central box) the modes experience an EF from 220 to 350 times.

Figure 5: Relative SERS enhancement factor for the 515, 633 and 785nm excitation wavelengths.

The colour lines are guide for eyes.

The maximum EF was obtained for the excitation at

785 nm, and joining 4 orders of magnitude for the bands at 450 cm-1, and decreasing of a factor of 10 (until 3 orders of magnitude) for the higher frequency modes. Thank to the colour lines, guide for eyes, is evident the new behaviour extrapolated by the SERS spectra: the maximum enhancement happens for visible-NIR region, 100 nm red shifted with respect to the peak of the LSPR profile.

The red shift of the near-field peak energies with respect to the far-field quantities is a well-known phenomenon in literature. It depends to the size of the particles, with larger particles displaying a more marked shift [15], but there is not a complete and simple

explanation in agreement with the experimental data that can be used for a quantitative prediction of the shift.

This work is a partial study, contribute for the PhD annual report, but it opens the way for future measurements and considerations. Our purpose is to extend the number of excitation wavelength. Using 532, 560, 660 and 695 nm excitation sources we can complete our multi-wavelength analysis and try to find the exact position of the maximum EF, since to obtain a complete profile to compare with the LSPR profile. At the same time, this experimental data may be of interest for theoretical calculations in order to clarify the connection between the far-field and the near-field point of view of the same effect.

Conclusion Multi-wavelength SERS measurements were carried

out on SERS active substrates of gold evaporated nanoclusters. The SERS intensities of the modes of the probe molecules, the Methylene Blue, were studied and compared with the corresponding Raman spectra.

Then, the SERS Enhancement Factor behaviour was compared with the Local Surface Plasmon Resonance profile of the substrate. The presence of Methylene blue soaked on gold nanoparticles causes an energy red shift and a broadening of LSPR profile, as known in literature, but the maximum enhancement was obtained for an excitation wavelength in the Near Infrared region (785nm), in spite of LSPR peak at 600 nm. These results open the way for further measurements and calculations for a better understanding about the differences between near and far field point of view, basics for a proper comparison between the LSPR and SERS profiles, and thus for the optimization of the enhancement factors.

Acknowledgments We acknowledge funding from the EU-FP7-NANOANTENNA project GA 241818 ―Development of a high sensitive and specific nanobiosensor based on surface enhanced vibrational spectroscopy‖ and the PRIN 2008 project 2008J858Y7_004 ―Plasmonics in self-assembled nanoparticles / Surface Enhanced Raman Spectroscopy on self-assembled metallic nanoparticles.‖

References [1] S. Nie and S. R. Emory, Science 275 (1997) 1102; [2] K. Kneipp et al., Chemical Physics 247 (1999) 155; [3] G. Laurent et al., Physical Review B 71 (2005) 045430; [4] E.C. Le Ru et al. Journal of Physical Chemistry C 112 (2008)

8117;


92

[5] H. Wang et al., Journal of American Chemical Society 127 (2005) 14992;

[6] E.C. Le Ru et al., Journal of Physical Chemistry C 111 (2007) 13794;

[7] G. Xiao and S. Man, Chemical Physics Letters 447 (2007) 305; [8] M. Kall et al., Journal of Raman Spectroscopy 36 (2005) 510; [9] K. Kneipp et al., Chemical Review 99 (1999) 2957; [10] E.C. Le Ru et al., Chemical Physics Letters 423 (2006) 63;

[11] A. Otto, Journal of Raman Spectroscopy 22 (1991) 743; [12] E.C. Le Ru et al., Current Applied Physics 8 (2008) 467; [13] S. Nicolai and J. Rubim, Langmiur 19 (2003) 4291; [14] A. McFarland et al., Journal of Physical Chemistry B 109 (2005)

11279; [15] J. Zuloaga and P. Nordlander, Nanoletters 11 (2011) 1280.


93

PHOTOLUMINESCENCE OF A QUANTUM EMITTER IN THE CENTER OF A DIMER NANOANTENNA: TRANSITION FROM THE PURCELL

EFFECT TO NANOPOLARITONS

N.Finaa,*, A.Ridolfob, O.Di Stefanoa,, O.M.Maragòc ,S.Savastaa

a)Dipartimento di Fisica della Materia ed Ingegneria Elettronica,Università di Messina, Viale F.S. D’Alcontres 31, 98166 , Messina, Italy

b) Technische Universitat Munchen, Physik Department, Germany. c) Istituto per i Processi Chimico-Fisici, Viale F. Stagno d’Alcontres 37, 98158, Messina, Italy


Abstract We present a fully quantum mechanical approach to

describe the light emitting properties of strongly interacting plasmons and excitons. Specifically we present calculations for ultracompact quantum systems constituted by a single quantum emitter (QE) (a semiconductor quantum dot) placed in the gap between two metallic nanoparticles. Light emitted by the quantum dot is shown to undergo dramatic intensity and spectral changes when the emitter excitation level is tuned across the gap-plasmon resonance. The resulting plexciton dispersion curve differs significantly from the one obtained via scattering experiments [1]. Our work suggests that the strong interaction between metallic nanoparticles and excitons can exploited for tailoring the spectral properties of quantum emitters for the realization of ultracompact colored and white LEDs.

Introduction The light-matter strong coupling regime is fascinating,

as it allows nonlinear quantum optics experiments to be done with as few as two photons, control of the direction of emission or phase of one photon with another one, the observation of single-atom lasing, the study and exploitation of quantum entanglement [2].

Here we investigate the emission properties of two Silver Metal Nanoparticles (MNP) with a Quantum Dot (QD) between these (see Fig. 1). In particular we study the modifications of the quantum emitter photoluminescence (PL) induced by the presence of the metallic nanoparticles (MNPs). We also study the transition from the weak to the strong coupling regime.

Fig.1 Dimer nanoantenna with quantum emitter. Entire system is embedded in an optically active

medium.

Theory The system is schematically showed in Fig1. It is

entirely embedded in a medium with constant permittivity

bε . The expectation value of the total system polarization is given by:

mP f a (1) where a is the destruction operator for the localized

surface SP mode, the QD dipole moment e d , and the coefficient f is given in Eq. (10). The term

is the expectation value of the lowering transition

operator eg . The QE and the MNP interacts via dipole-dipole coupling.

States g e transition is resonantly coupled with the localized surface plasmon dipole mode with a strength g, as showed in Fig 2.


94

Fig 2. Quantum emitter two level representation: external optical pump excites ground QD states,

giving rise to excitonic emission of light caused by interaction with MNPs-SP.

Electrons are optically or electrically pumped from

lower levels j to upper levels i , then decay

nonradiatively to level e . Electrons finally decay by

spontaneous emission to level e .The full quantum dynamics of the coupled nanosystem can be derived from the following master equation for the density operator,

X sp( , )Si H L L (2) Where SH represents the Hamiltonian terms including

free dynamics, interaction and driving, i.e.:

S 0 int driveH H H H (3) with

† †0 sp xH a a (4)

where x and sp are the energies of the QD excitonic and MNP plasmonic transitions. Eq.(4) represents the free system Hamiltonian equal to the sum of free MNP system term with free QE term. The Hamiltonian term describing the interaction between the QD exciton and the quantized SP field, in the rotating wave approximation reads:

† †int ( )H i a ag (5)

Where:

g (6)

being

30

4 6 '(8 1)Q r

(7)

a field term related to the whole system, and, where:

3

3

RQS r

(8)

with 1, 2 ,S whether the field polarization is

parallel or orthogonal to the R direction [3], while ' is a parameter depending on SP resonance frequency. The system excitation by a classical input field can be described by:

† * †

drive 0 0( ) ( )H E a a E (9) Notice that 0E is different from zero only in scattering

calculations. The Markovian interaction with reservoirs determining the decay rates xγ and spγ for the QD exciton and the SP mode respectively, as well as the pumping mechanism of the QD, is described by the Liouvillian terms, XL and spL [4]. Furthermore we found that the term related to interaction of MNPs-SP with incoming field is f , and it‘s given by:

3b0

48iQ 2 '(1 8 ) 3

f rQ

(10)

Results We have calculated the PL on a system with a 6nm

radius MNP at a distance R = 9.5 nm embedded in a medium with a dielectric constant bε = 3.


95

Fig.3 : Calculated dimer nanoantenna-QE PL spectrum for different dipole moments.

In Fig.3 we can see how, on increasing the QD dipole

moment, the splitting between the two PL peaks enhances [5]. This is due to the fact that the Vacuum Rabi Splitting (VRS) limit is given by the following condition:

x sp(γ +γ )2

2g (11)

and, because, from Eq.(6), g is related to dipole

moment, on increasing of it, will increase the VRS, as shown by PL spectra.

The PL spectra achieved at different distances between the two MNPs, tuning the exciton frequency on the resonance MNP-SP frequency, with a dipole moment μ/e =0.7nm, are shown in Fig.4. We can see how, on increasing the distance QE-MNP, strong coupling plexcitonic effect, progressively, vanishes, until to show only the QD dipole row (on R=28nm).

Fig.4 : PL spectra calculated for different distances centered at frequency a . On increasing distances the double peak splitting

disappears. A dipole moment μ/e =0.7nm has been used.

The influence of MNPs on the PL of quantum emitter

has been studied in the weak coupling regime [7]. Here we addressed the situation where the interaction between the emitter(s) and the MNPs is so strong that a perturbative approach fails. Figure 5 displays a series of PL spectra taken at different exciton-SP energy detuning. The typical anticrossing behavior, characteristic of the strong coupling regime, can be observed. At large detunings the PL emission is concentrated at the transition energy of the emitter.


96

Fig.5. PL spectra taken at different exciton-SP energy detuning.

When the transition energy approaches the SP resonance, two emission peaks are clearly visible and emission is shared by the two polariton modes. For comparison, Fig. 6 shows scattering spectra [6] which display a different behavior and a different normal mode splitting.

Fig.6. Scattering spectra as a function of the exciton resonance.

Conclusions We have investigated for the first time light emission

properties of QEs strongly coupled to MNPs. When strong coupling is achieved, light emitted by the QD is shown to undergo dramatic intensity and spectral changes when the emitter excitation level is tuned across the gap-plasmon resonance. The resulting plexciton dispersion curve differs significantly from the one obtained via scattering experiments. This work suggests that the strong interaction between metallic nanoparticles and excitons can exploited for tailoring the spectral properties of quantum emitters for the realization of ultracompact colored and white LEDs.

References [1] A. Ridolfo et al., Phys. Rev. Lett. 105, 263601 (2010); [2] Kimble, H. J. Strong interactions of single atoms and photons in

cavity QED. Phys. Scripta 76, 127–137 (1998); [3] S.A Maier Plasmonics: Fundamentals and applications, Springer; [4] M.O. Scully, M.S. Zubairy, Quantum Optics, Cambridge

Univ.press; [5] G.Khitrova et al. Nature Physics 2, (2006); [6] S.Savasta et al., ACS Nano 4 (11)(2010), pp. 6369 6376 [7] L.Novotny,B.Hecht, Principles of Nano-Optics, Cambridge

Univ.pres


97

LATERAL DIFFUSION OF DPPC AND OCTANOL IN A LIPID BILAYER MEASURED BY PFGE NMR SPECTROSCOPY

S. Rificia,*

a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F.S. D’Alcontres ,98166 S. Agata-Messina, Italy * Corresponding author, e-mail: [email protected]

Abstract Lipid lateral diffusion coefficients in the system of 1,2-

palmitoyl-sn-glycero-3-phosphocholine (DPPC), Octanol and water were determined by the pulsed field gradient NMR technique on macroscopically aligned bilayers. The molar ratios between DPPC and Octanol and between DPPC and water were set to 1:2 and 1:28 respectively. The temperature was varied between 270 K and 323 K.

Introduction Cell membrane is the first part of the cell to be in

contact with any nutrient or pathogen in the extracellular matrix. Biological membranes are complex mixtures of different lipid molecules and proteins. A lipid is an amphiphilic molecule with an hydrophilic polar headgroup and usually two hydrophobic hydrocarbon chains. When dispersed in an aqueous environment, lipids self-assemble in order to reduce contacts with water. They can arrange themselves in a variety of morphologies depending on the structure of the lipid, the nature of the lipid headgroup and its degree of hydration, temperature, concentration and osmotic pressure. Multilamellar vesicles, continuous ordered bilayers and monolayers, liposomes and micelles are typical examples of possible structural arrangements. [1]

Single artificial phospholipid, or simple mixtures of artificial phospholipids have long been used as mimetic membranes for examining the physical, chemical and biological properties of the biomembranes. This approach is justified by the observation that some model membrane systems have been widely recognized as essentially equivalent to natural systems such as those found in myelin and erythrocyte membranes. [2]

Dipalmitoylphosphatidylcholine (DPPC) has a very simple chemical structure, a phosphocoline (PC) headgroup and two identical linear saturated hydrocarbon chains, and plasma membrane contains a relatively large amount of phospholipids with PC headgroup, this is why DPPC is so largely used in all studies about model membrane. Despite it has been widely studied, his dynamics are still not well understood.

Many structural and dynamic intrinsic properties of aqueous dispersions of lipid bilayers are governed by temperature. In the case of phosphatidylcholines, these phase transitions take place within the temperature range 263–353 K, depending on the strength of the attractive

Van der Waals interactions between adjacent lipid molecules. Longer tailed lipids have more area to interact, increasing the strength of this interaction and consequently decreasing the lipid mobility. Transition temperature can also be affected by the degree of unsaturation of the lipid tails. An unsaturated double bond can produce a kink in the alkane chain, disrupting the lipid packing. This disruption creates extra free space within the bilayer which allows additional flexibility in the adjacent chains. [3]

DPPC shows three kinds of structural changes with increasing temperature under atmospheric pressure. This changes are thermotropic phase transitions: the sub-transition from the lamellar crystal (Lc) phase to the lamellar gel (Lβ′) phase, the pre-transition from the Lβ′ phase to the ripple gel (Pβ′) phase, and the main transition from the Pβ′ phase to the liquid crystalline (Lα) phase occur in turn with increasing temperature. [4]

The (Lα) phase is considered the most important, because many biologically relevant processes occur in this phase. Indeed, lamellar bilayers in the fluid phase supply an efficient, planar permeability barrier, which still allows functional flexibility and lateral diffusion motions of associated membrane proteins.

Adsorption of alcohol molecules or other small amphiphilic molecules in the cell membrane has a destabilizing effect on its structure. Experiments on phospholipid membranes have shown that alcohol molecules can induce the interdigitated phase [5] that, at high alcohol concentrations, replaces the ripple gel phase [6,7]. A complete interdigitation is expected at alcohol concentrations above a threshold value assumed to be about 2:1 alcohol to lipid ratio in the membranes as it has been observed for DPPC/n-butanol system by a DSC study [7]. When the interdigitation occurs, lipid molecules from opposing monolayers interpenetrating, thereby decreasing the bilayer thickness. The increase of the polar headgroup area, due to the addition of alcohol molecules, gives rise to a reduction of the Van der Waals attraction between lipid acyl chains. Bound alcohol molecules reduce the mobility of the polar headgroups and, at the same time, cause a decrease of the ordering and an additional coiling of the melted acyl chains.

Concerning dynamics, different types of motions, with correlation times ranging from picoseconds (corresponding to the motion of lipid chain defects, for example) to microseconds (corresponding to collective excitations of the bilayer membrane), characterize


98

bilayers, a large variety of which is essential for the functionality of membranes [8,9,10].

Motions within the bilayer plane have been largely studied by NMR relaxation techniques [11,12,13] and neutron scattering [8,9,10].

Experimental details - Sample preparation The phospholipid 1,2-palmitoyl-sn-glycero-3-

phosphocholine (DPPC) was purchased from Avanti Polar Lipids, Octanol was purchased from Sigma Chem. Co. Both chemicals were used without further purification.

Aligned multilayers of DPPC with Octanol were obtained following the preparation suggested by Hallock [14], using mica plates as supporting substrate. Mica substrate was covered with about 1.5 mg of lipids per cm2. Following the cited procedure, DPPC and Octanol were dissolved in an excess of 2:1 CHCl3/CH3OH (chloroform/methanol). The solution was spread and dried on the face of the substrate plate. All procedures for sample preparation were executed in a glove box under nitrogen gas to prevent lipid oxidation. This procedure resulted in a thin film covering the whole area of the mica plate. The sample was indirectly hydrated at 323 K in 96% relative humidity using a saturated potassium sulfate D2O solution for 12 days, after which 28 mole of D2O per mole of lipid were added. The mica plate was then placed in a glass tube in the diffusion probe.

Nuclear magnetic resonance Self diffusion coefficients of hydration water ( WD ),

DPPC ( D ) and Octanol ( OcD ) molecules were measured by hydrogen pulsed-field gradient spin echo NMR (1H-PGSE-NMR), which enables the non-invasive measurement of molecular self diffusion coefficient over a wide range of time scales (from milliseconds to seconds) directly [15, 16].

PGSE experiments were performed on aligned pure DPPC and DPPC with Octanol membranes deposited on mica sheets. All measurements were carried out in fully hydration condition at temperatures below, near and above the phase transition temperature using a Bruker AVANCE NMR spectrometer operating at 700MHz 1H-resonance frequency. The temperature was controlled within ± 0.5 K by a heated air stream passing the sample.

Self-diffusion measurements are based on NMR pulse sequences, which generate a spin-echo of the magnetization of the resonant nuclei. The method is based on sensitising the sample to molecular translational displacement by the application of magnetic field-gradient pulses.

By the appropriate addition of two pulsed-field gradients, in the defocusing and refocusing period of the sequence, of duration δ and intensity g, separated by a time interval Δ, the spin-echo intensity becomes sensitive

to the translational motion along the gradient direction for the tagged molecules. These gradients, in fact, cause the nuclear spins in different local positions in the sample to precess at different Larmor frequencies, thereby enhancing the dephasing process. If the spins maintain their positions throughout the experiment, they will still refocus completely into a spin–echo by the SE pulse sequence. On the other hand, if they change their positions during the experiment, their precession rates will also change, and the refocusing will be incomplete, resulting in a decrease in the intensity of the spin–echo.

The spin echo M(δg,Δ), is attenuated according to

20/ exp[ ]M M DQ (1)

where Q g and γ is the gyromagnetic ratio of 1H. Q has the dimension of an inverse length, being a measure of the spatial scale probed, and is equivalent to the exchanged wave vector in a scattering experiment.

In our experiment, the mica plate with deposited DPPC with Octanol is placed parallel to the magnetic field to test for lateral (in-plane) diffusion. To record the decay of the 1H components, a train of pulses at increasing gradient strength is used.

Integration of spectral peaks was performed using the Bruker-supplied XWIN-NMR software.

Figure 1 shows the decay of spin-echo intensities for water and phospholipid/alcohol system as a function of Q2Δ for three different temperatures, T=287K (triangle), T=291K (circle) and T=295K (square). In the same figures, the fitting curves (continuous lines), obtained from a nonlinear fit of the Fourier-transformed peak amplitudes according to the Equation (1), are also shown.

The data were fitted to an equation with three diffusion coefficients. This would be the case for a system consisting of three separated species. In fact, three decay times are clearly visible, the faster due to water molecules, the lower to phospholipid molecules, and the intermediate ascribed to Octanol molecules.

The found diffusion coefficients for WD , D and OcD are reported in Table 1.

Table 1

T=287K T=291K T=295K

2 /WD m s 103.4 10 103.8 10 105.1 10

2 /OcD m s 116.5 10 117.1 10 101.3 10

2 /D m s 127 10 125.3 10 111 10


99

1E8 1E9 1E10 1E11

0.1

1

DPPC+Octanol

M /

M0

Q2 Delta [m 2 sec]

T=287 K T=291 K T=295 K Fit

Figura 1: PGSE intensity decay in fully hydrated

DPPC/Octanol bilayer at T=287K (triangle), T=291K (circle) and T=295K (square). The

continuous lines are the fitting functions.

In the case of water molecules, we found diffusion

coefficients in good agreement with those measured in PC-water systems, which are in the range of

10 21 10 /m s to 10 220 10 /m s depending on water concentration, temperature, and bilayer composition. [17, 18,19,20,21,22].

Figure 2 shows the three diffusion coefficients as a function of T.

It can be observed that the lateral diffusion coefficient increases with increasing temperature; i.e. when the full system is clearly in the liquid–crystalline phase, where enhanced dynamics of the acyl chains are expected.

Water and alcohol molecules follow membrane transition. Alcohol diffusion sharply lowers near the main transition temperature, and, below the transition, it seems that alcohol and DPPC molecules have the same diffusion coefficient. Below the transition, Octanol and DPPC move together, and this is an evidence of the formation of the interdigitated phase. Conclusions

1H-PGSE-NMR experiments provided information on long-range lateral diffusion, up to some mm distances, of inter-layer water, lipid and Octanol molecules.

Three decay times are clearly visible, the faster due to water molecules, the lower to phospholipid molecules, and the intermediate ascribed to Octanol molecules.

In the case of water, a reduction in the diffusion coefficient alone is observed and assigned to restricted geometry.

On the other hand, the phospholipid component shows a novel and interesting result of a nearly constant diffusion coefficient in the gel phase and a net increase in mobility in the liquid–crystalline phase.

275 280 285 290 295 300 305 310 315 3200.0

2.0x10-10

4.0x10-10

6.0x10-10

8.0x10-10

1.0x10-9

1.2x10-9

D (m

2 /sec

)

T(K)

DW

DOc

D

Figura 2: The three self diffusion coefficients of

hydration water (circles), DPPC (stars) and Octanol (triangles) as a function of T are shown. The self diffusion coefficient of bulk water (empty

circles) in also plotted.

Below the transition, Octanol and DPPC move

together, and this is an evidence of the formation of the interdigitated phase.

References [1] R. Lipowsky and E. Sackmann, Handbook of Biological Physics,

Vol. 1, Elsevier Science, Amsterdam, 1995; [2] Rosser, M. F. N., H. M. Lu, and P. Dea. 1999, Biophys. Chem.

81:33–44; [3] R. Koyonova and M. Caffrey, Biochim. Biophys. Acta 1376

(1998) p.91; [4] N Tamai, M Goto, H Matsuki, S Kaneshina, Journal of Physics:

Conference Series 215 (2010) 012161 doi:10.1088/1742-6596/215/1/012161;

[5] J. L. Slater and C. H. Huang, Prog. Lipid Res. 27, 325-359 (1988); [6] E. S. Rowe, T.A. Cutrera, Biochemestry 29, 10398-10404 (1990); [7] F. Zhang and E. S. Rowe, Biochemistry 31, 2005-2011 (1992); [8] M.C. Rheinstadter, T. Seyde, L. Demmel et al., Phys. Rev. E 71

(2005) p.061908; [9] M.C. Rheinstadter, C. Ollinger, G. Fragneto et al., Phys. Rev. Lett.

93 (2004) p.108107; [10] S. Konig, W. Pfeiffer, T. Bayerl et al., J. Phys. II (1992) p.1589; [11] S. Konig, T.M. Bayerl, G. Coddens et al., Biophys. J. 68 (1995)

p.1871; [12] G. Oradd and G. Lindblom, Biophys. J. 87 (2004) p.980; [13] P. Meier, E. Ohmes and G. Kothe, J. Chem. Phys. 85 (1986)

p.3598; [14] Hallock K J, Henzler Wildman K, Lee D K and Ramamoorthy A

2002 Biophys. J. 82 2499–503; [15] E.O. Stejskal and J.E.Tanner, J. Chem. Phys. 42 (1965) p.288; [16] H.V. As and P. Lens, J. Ind. Microbiol. Biotech. 26 (2001) p.43; [17] Lange, Y., and C. M. Gary Bobo. 1974, J. Gen. Physiol. 63:690-

706; [18] Inglefield. P. T., K. A. Lindblom, and A. M. Gottlieb. 1976,

Biochim. Biophys. Acta. 419:196-205; [19] Lindblom, G., H. Wennerstrom, and G. Arvidson. 1977, J. Quant.

Chem. 12(2):153-158; [20] Chan, W. K., and P. S. Pershan. 1978, Biophys. J. 23:427-449; [21] Konig, S., E. Sackmann, D. Richter, R. Zorn, C. Carlile, and T. M.

Bayerl. 1994, J. Chem. Phys. 100:3307-3316; [22] Volke, F., S. Eisenblatter, J. Galle, and G. Klose. 1994, Chem.

Phys. Lipids. 70:121-131.


100


101

CHEMICAL EQUILIBRATION OF THE QUARK GLUON PLASMA

F.Scardinaa,b,*, M.Colonnab, V.Greco,b,c, M.Di Torob a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F.S. D’Alcontres ,9816 S. Agata-Messina, Italy

b) INFN Laboratori Nazionali del Sud, Via S. Sofia 62, I-25125 Catania, Italy c) Dipatimento di Fisica e Astronomia, Università di Catania, Via S. Sofia 64, I-95125 Catania, Italy


Abstract The ultra-relativistic heavy ion collisions performed at

the Relativistic Heavy Ion Collider (RHIC) and at Large Hadron Collider (LHC) represent the fundamental tool to study the properties of the Quark Gluon Plasma (QGP). We have studied the evolution of the QGP created in such collisions using a relativistic transport code which is based on the solution of the relativistic Boltzmann equation including elastic and inelastic two body collisions between partons. We have focused our attention on the chemical equilibration of the QGP. In fact such equilibration is a fundamental step to deal with before to analyze hadronization. We have performed calculation in a box at equilibrium in order to check the code and finally we have performed simulation for the collision in both RHIC and LHC case. The purpose of our work is to show how the QGP, which is initially composed for mostly by gluons, go towards chemical equilibrium with a consequent enhancement of the quarks number. Moreover we have studied the dependence of the chemical equilibration from the transverse momentum pT. We have observed that at the end of the evolution of the fireball the ratio Nq/Ng in the region of low pT reach the equilibrium value of 2.25. The presence of a such large amount of quarks should modify the background for the various energy loss scenarios. The ratio between the quark number and the gluon number in the region of high pT do not reach the equilibrium value but is significantly different from the initial value. This difference should explain the relative abundances of the hadrons that coming from the fragmentation of high pT partons.

INTRODUCTION We have studied the evolution of the QGP created in

ultra-relativistic heavy-ion collision with a relativistic transport code based on the numerical solution of the relativistic Boltzmann. Using such code we have studied the chemical equilibration of the QGP created at RHIC and at LHC. The analysis of such equilibration assume a fundamental importance in order to have a comprehension of the abundances of the different species of hadrons revealed in the experiment. Moreover we want to improve the description of the QGP using an effective kinetic theory for a quasi-particle model. In such model the particle acquire an effective mass and this causes a further enhancement of the quark number.

TRASPORT APPROACH We have studied the evolution of the Quark Gluon

Plasma using a relativistic transport simulations based on the solution of the Boltzamann equation.

22( , )p f x p C (1) Where f(x,p) are the partons distributions functions and

C22 is the collision term.

' '

32

22 31 2

3 ' 3 '' '1 2

1 2 1 23 ' 3 '1 22 4 4 ' '

1 2 1 212 12

1 12 (2 ) 2

( )(2 ) 2 (2 ) 2

(2 ) ( )

d pCE E

d p d p f f f fE E

M p p p p

(2)

υ is set equal to 2 if 1 and 2 are identical particles. For the implementation of the collision integral we use

the so called stochastic algorithm[1,2]. In such algorithm if the collision will happen or not is sampled stochastically comparing the probability of the two body

collision with a random number between 0 and 1.

2 2

22 22 31 2

collrel

N tP vN N x

(3)

If the extracted number is less than the probability the

collision will occur. In the limit Δt ->0 Δx->0 the numerical solutions using the stochastic method converge

To the exact solution of the Boltzamann equation. So it is important to divide the space into sufficient small cells.

We consider both elastic and inelastic collision using the differential cross section indicated in the following formulas [1,3]

2

2 2 2 2

2( )

gg ggs

T T D

ddq q q

(4)


102

2

2 2 23 ( )

gg qqs

T T q

ddq s q m

(5)

2

2 2 2

6427 ( )

gg qqs

T T q

ddq s q m

(6)

Where qT is the transverse component of moment

transfer, mD and mq denote respectively the Debye mass for gluons q and quarks respectively.

Calculations In a Box at equilibrium With the purpose of demonstrate the correct operation

of our code we have chosen some situation in which the outcome are known analytically. Hence we have performed ―box calculations" in which a particle ensemble is enclosed in a box, with fixed limits, and evolve dynamically until an appropriate final time. Initially particles are distributed homogeneously within the box and their momentum is chosen highly anisotropic

( 6 ) ( )T zT z

dN p GeV pNdp dp

(7)

After a sufficiently long time the system equilibrate as

shown in fig. 1. For a classical, ultrarelativistic ideal gas the energy distribution has the Boltzmann form

/

2 3

12

E TdN eNE dE T

(8)

In figure 1 the time evolution of the energy distribution

for such box calculations is depicted the size of the box is 125 fm3. We have considered anisotropic calculations and we have taken a constant cross section of mb. The final time is 3 fm/c. Moreover in order to improve statistics we have used 50 test particles for one real. The dotted line in the figures indicate the analytical distribution with temperature T=2 GeV calculated using

The following formula

3 T (9) Where the energy density and the particle densities are

given by the initial conditions. We see a good agreement between the numerical results and the analytical distributions. As we can observe from the figure our code reproduce analytical results. In order to have sufficient argument to guarantee whether our algorithm operating correctly is necessary to check other quantity, as for example the time evolution of momentum anisotropy shown in fig. 2 and defined as the average transverse momentum squared

over the average longitudinal momentum squared. The initial conditions in this case are set to be the same as in fig 1.

Figure 1:Temporal evolution of energy distribution of a system consisting of N=2000 massless

particle in a fixed box whose size are 125 fm3

Figure 2: Time evolution of the momentum anysotopy from box calculations. The initial conditions are set to be the same as in Fig. 1

Once we have checked that our algorithm reproduce the

analytical calculation relatives to kinetic equilibrium we have checked that also the chemical equilibrium of the plasma can be reproduced by our algorithm.

For massless case the ratio between the number of quark and the number of gluon is simply given by the ratio between the respective degrees of freedom υ

q q

g g

NN

(10)


103

where υq=2*3*Nf υg = 2*8. In our case we consider two flavour and thus the ratio between the number of quark and the number of gluons is 2.25. The results are shown in fig.3

Figure 3:Time evolution of the gluon and quark number in box calculations. We have considered gluons and quarks with three flavour as parton

species

Results for the heavy Ion collision We have performed simulations for heavy-ion

collisions for both RHIC (200 AGeV) and LHC (5.5 ATeV). In figure 4 are shown the ratio between the number of quark and the number of gluons as a function of transverse momentum. The dot line indicate the initial ratio while the thick line and the dashed line indicate the final ratio obtained at RHIC and LHC respectively. We can observe that for both RHIC and LHC at low transverse momenta the ratio is near to the equilibrium value. Moreover at LHC where the evolution time is longer also at high pT the ratio is different from the initial one

Figure 4: Ratio between the quarks number and the gluon number as a function of pT

EFFECT OF THE MEAN FIELD We have the intention to introduce in our code the

effect of the mean field using a quasi-particle model [4]. In such a model the interaction is encoded in the quasi particle masses and once the interaction is accounted for in this way the quasi particle behave like a free gas of massive constituents.

The effect of the masses on the chemical equilibration of the plasma is substantial.

In the massive case the ratio Nq/Ng depends on the temperature as can be calculated in the following formula

2

2

/

22

/

q

g

q Tq qm T

q q

g g g Tg gm T

md e

TNN m

d eT

(11)

Where

2 2 2 21 1;q q g gm p m pT T

(12)

The expected ratio is indicated in fig. 5. In this figure

we can observe that the value of the ratio is strongly dependent from temperature and that at the freeze-out temperature the ratio reach the value of 6.3 that is larger that the value obtained in the massless case.

Figure 5: ratio Nq /Ng as a function of temperature calculated using the formula 0.8

Conclusions The Quark Gluon Plasma created in heavy-ion collisions seem to reach chemical equilibrium at low transverse momentum, but in the case of LHC also at high pT the ratio is significantly different from the initial one. Thus at the end of its evolution the number


104

of quark in the plasma is greater than the number of gluons and this have two important implication: first of all the background of the energy loss process is significantly modified and moreover the abundances of the different species (pion, proton , kaon) coming from the fragmentation of quarks and gluons are significantly affected by the increasing of the quarks number. In the region of high transverse momenta this effect must be analyzed in order to have a better comprehension of the different suppression experienced by the hadronic species and have to be compared with the results of the [5,6,7]. We have moreover the intention to include the effect of the mean field in order to give a better description of the QGP. This will be done using a quasi-particle model.

We expect that the effect of the masses will increase the ratio between the quark number and the gluon number up to 6 for the region of low pT . This implicate that the bulk should be for mostly composed by quarks.

REFERENCES [1] Z. Xu , C. Greiner, Phys. Rev C.71 (2005) 064901; [2] G. Ferini , M. Colonna, M. Di Toro and V. Greco, Phys. Lett. B

670, 325 (2009); [3] J. F. Owens, E. Reya, and M. Gluck, Phys. Rev. D 18, 1501

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73.


105

A STUDY ABOUT DYNAMIC MODELS ON PHOSPHOLIPIDS

A. Trimarchia,* a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F.S. D’Alcontres ,9816 S. Agata-Messina, Italy


Abstract Model membranes are a first step to understand very

complex objects like cell membranes. The former constitute a essential element so that cells work. Membranes are active protagonists in many processes, as material transport and cell signaling. The comprehension of the dynamics in play can give us the possibility to exploit them in several research fields like pharmaceutical industries or medical sciences. In this paper we try to explain some membrane motions by applying several models to the elastic incoherent scattering factor (EISF) like the spherical diffusion or the uniaxial rotation and we show the results.

Introduction Membranes are an essential part of the living organisms, playing a fundamental role in several tasks[1]: they surround cells separating them from the external environment. They are composed of amphipathic phospholipids: a hydrophilic head and one or two hydrophobic chains. In a biological membrane there are many different types of lipids as well as many other components besides them, like the proteins, that have important tasks as surface recognition, cytoskeleton contact, signaling, enzymatic activity, or transporting substances across the membrane. Membranes are an important site of cell-cell communication. The complexity of these objects makes their study very difficult so we approximate them with more simple structures, phospholipid bilayers. Phospholipids undergo phase transitions in the temperature range from -10 to 80 °C; the main phases belonging to bilayers are the gel phase where the chains are stiff and well ordered, and the liquid phase where the chains are quite disordered. The structures that these phospholipids can form are several ones, depending on lipid concentration, temperature, pressure, and the presence of other substances: they can form bilayer structures, spherical structures, like liposomes, or micelles[2,3]. Dimensionally, important structural quantities to characterize a phospholipid bilayer are the lamellar repeat spacing D, the hydrocarbon chain thickness 2Dc and the average area per lipid A. NMR, X-ray and neutron diffraction[4-6] techniques provided several information about form factors, electron density and scattering length density profiles, while further information and confirmations to experimental models are been obtained by simulations[7]. Nowadays membranes are objects of studying for several research fields and applications[8,9]. In this paper we focus our attention on a

QENS study of DMPC(1,2-dimyristoylsn-glycero-3-phosphatidylcholine), and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) phospholipid bilayer, in order to investigate dynamics.

Experimental details

SAMPLE PREPARATION DMPC and POPC powder sample were purchased from

Avanti Polar Lipids. The samples were prepared in order to obtained aligned multilayers following the preparation suggested by Hallock et al.[10]. The lipids were dissolved in a solution 2:1 CHCL3/CH3OH (chloroform/methanol). After drying the lipid solution, it was joined to a solution 2:1 CHCL3/CH3OH containing a 1:1 molar ratio of naphthalene (C10H8) to lipid so that for each mg of substrate the lipid was dissolved again in 15 μl of this solution. This solution was applied on only one face of the mica sheets, so that we spreaded about 1,5 mg of lipid per cm2. Naphthalene and any residual organic solvent were removed by means of a vacuum drying overnight. Hydration at 40 °C in 96 % relative humidity was indirectly performed using a saturated potassium sulfate D2O solution for 12 days, after which 28 moles of D2O per mole of lipid are added. Each sample was then built up stacking 6 substrate plates piled with the last foil not spreaded, and was equilibrated at 4 °C for 12 additional days. The alignment was then verified by 31P-NMR chemical shift and with X-ray diffraction.

SPECTROMETER The IN5, time of flight (TOF) spectrometer, at ILL

Facility (Grenoble), has been used to perform neutron scattering measurements on the phospholipids. This instrument is used to study low-energy transfer processes as a function of momentum transfer, typically, in the region of small energy and momentum transfer values, with an energy resolution of the order of δE/E = 1% (e.g. quasi-elastic scattering in solids, liquids, molecular crystals and inelastic scattering with small energy transfers in the order of magnitude 0.1-250 meV). It is characterized by a primary spectrometer in which two synchronized choppers are used to define the incident beam energy, while a third chopper removes unwanted neutrons. A fourth chopper, finally, turning with lower velocity, avoids different pulse overlap. Samples, usually, were run in two orientations for the normal to membrane plane and beam direction.


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At θ = 135°, the dynamics are mainly probed in the membrane plane. All scans have been performed starting from an equilibrated liquid crystalline phase hydrated with 28 D2O molecules per lipid.

Figure 6:Data fits of DMPC sample at 307 K and POPC sample at 298K in 135° orientation. Data

have a resolution of 37μeV. Spectra representation is in logarithmic scale to better display

lorentzians.

DATA ANALYSIS

Experimental data have been collected on IN5 at a

resolution of 37 μeV and with a wavelength λ =8Å. We have measured DMPC+28 D2O multi bilayer sample at T = 307 K and POPC+28 D2O multi bilayer sample at T = 298 K and both are in liquid phase. Both measurement have been performed in the 135° orientation that gives us information about in-plane motions. Treatment data have been executed with LAMP software, in order to remove bad spectra, correct cross-sections and rebin in energy the time of flight obtained data; afterwards they have been fitted by performing a linear least-square analysis and using Minuit program.

The line shape is well represented by the sum of a Delta function and three Lorentzian functions convoluted with

the instrumental resolutions. We have assumed as fit parameters the areas of the four functions and the half width at half maximum (HWHM) of the three lorentzian curves:

21 2 2 2

2

3 43 42 2 2 2

3 4

( ) ( )I A A

A A (1)

It is interesting to notice that this model fits very well

the experimental data as it is clear from the Figure 1 where a semi logarithmic plot is displayed to put the emphasis on residues.

From fit parameters of DMPC and POPC it is evident as the A1, the area of the Gaussian curve (Figure 2), is decreasing with Q. This means that in both case, the dynamics is confined. Furthermore, the HWHMs of the two phospholipids shows us three different dynamics belonging to systems, in so far occur on different time-scales and the specific rates of each one differ from other ones at least an order of magnitude (Figure 3).

From the areas with several mathematical passages, we can obtain the EISFs of the three motions for the two systems; in particular the fast motion EISF can be obtained easily like 1-A4. Several models can be used to fit these quantities and obtain information about dynamics concerning the sample and its spatial displacement.

Figure 2: POPC areas: the A_1 component (Delta contribution) highlights a confined dynamics.

EISFs have been fitted with suitable models by means of Mathematica® software.


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Figure 3:HWHM of the three motions. Diffusion (dark points) and rattling motion (blue points).

EISF corresponding to the first lorentzian with HWHM

= 10-12 µeV can be considered to belong to a diffusion of the atoms around their position[11]. The motion characterized by a HWHM of about 2000 µeV is believed to be a fast rotation, called also rattling motion around the molecule axis. The model applied to the corresponding EISF is the uniaxial rotation model[12]:

2 2

0(2 1) ( ) ( )m m

mEISF m j QR S (2)

where

0

( )2sinh

(cos )exp( cos )

m

m

S

P d (3)

is an order parameter e Pm is the Legendre polynomials

of order m. The δ parameter provides information about how the

motion of the atom has a distribution in a direction: greater the parameter, more directional the distribution[13]. A limit case is δ = 0 that corresponds to an uniform distribution.

The EISF concerning the HWHM of about 100 µeV is not quite clear yet, and other studies are requested to give it an accurate meaning.

For the experimental setup specifications, free diffusion of lipids is too slow to be observed, and it is hidden inside the experimental resolution. In literature, there are several models to explain these motions. The slow motion is considered like a diffusion in a restricted volume or, or like a ballistic motion with a long range transport on a nanometre scale with a Gaussian-like model[14-16]. The fast motion is considered like a rattling motion [15], while

the intermediate dynamics is thought like a kink motion, a combination of a rotation plus an out of plane diffusion[14].

Experimental results

From the above relations the shape of the three EISF can be determined (Figure 4).

A comparison between POPC and DMPC EISFs (in particular in Figure 5 diffusion EISF) shows as for all three motions the POPC structure factors are always higher than DMPC ones. This means POPC is characterized by a dynamics slower than DMPC one; hypothesis about this experimental fact can be ascribed to acyl chains more long in the POPC, and then a more molecular weight; the presence of a double bond between carbon atoms in one of this POPC chain could likely entail a decreased mobility of the whole system.

Figure 4: EISF of the motions concerning the hydrogen atoms of the fatty acid chain of POPC.

The EISF corresponding to rattling motion is displayed

in Figure 6 with the fit curve. The formula (2) was cut off after sixth order to calculus limits of the computer used to run Mathematica. The value of R in the formula was inserted like a constant and equal to the C-H bond length: R = 1.1 Å. The formula was modified with the adding of a normalization parameter, A, to have at Q = 0 Å-1 an unitary value of EISF. The model fits quite well both EISF samples and provides for the parameters the following values; for DMPC sample, δ = 2.45, A = 0.1997, while for POPC sample, δ = 1.95, A = 0.248. In the case of DMPC, the experimental points from Q = 1,4 Å-1 to 2.2 Å-1 have been adding from DMPC data obtained in an experiment with wavelength λ = 5 Å. The fit results tell us that the distribution is quite uniform, in particular for the DMPC sample.


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Figure 5: EISF comparison between POPC and DMPC samples

Figure 6: Fit of the EISF of the rattling motion with the uniaxial rotation model.

Conclusion

This work has highlighted like our phenomenological model fits very well experimental data bringing out the presence of three distinct motions that involve hydrogen atoms of the phospholipidic hydrophobic chains: an hampered rotation, that we can indicate like a rattling motion, of the hydrogen atom around its position. The other two motions need further studies and the application of other models to be identify with more clarity. The phenomenological model which we have proposed to fit data has provided similar results to other ones available in bibliography[13-18]. The uniaxial rotation model applied to the EISF of the rattling motion gave us information about its distribution width. Successive studies will deal with investigations in normal direction to the membrane (45° orientation) and evaluations of these motions at different temperatures to observe, i. e., how dynamics behaves in the gel phase. A further study will take in consideration the interdigitation of alcohols between

phospholipids in order to observe their influence on this system.

References [1] R. Lipowsky, E. Sackmann. (1995) Structure and Dynamics of

membranes: from cells to vesicles. Handbook of Biological Physics, Vol 1;

[2] Jain, M., Introduction to Biological Membranes, 2nd ed., John Wiley & Sons, New York, 1988;

[3] Gennis, R.G., Biomembranes. Molecular Structure and Function, Springer-Verlag, New York, 1989;

[4] G. Buldt et al., J. Mol. Biol., 134, 673, 1979; [5] G. Zaccai et al., J. Mol. Biol., 134, 693, 1979; [6] J. N. Sachs et al., Biophys. J., 100, 2112, 2011; [7] I. Z. Zubrzycki et al., J. Chem. Phys., 112, 3437, 2000; [8] Immordino ML, Dosio F, Cattel L., Int. J. Nanomedicine 1 (3)

(2006) 297–315; [9] Dagenais, C. et al., Eur. J. Phar. Sci., 38(2) (2009) 121-137; [10] K. J. Hallock et al., Biophys. J., 82, 2499, 2002; [11] V. F. Sears, Can. J. Phys. 45, 237 (1967); [12] B. F. Mentzen, Mater. Res. Bull., 1987, 22, 337; [13] M. Bee, Quasielastic Neutron Scattering; Taylor & Francis: 1988; [14] Sackmann, E., Konig, S., Pfeiffer, W., Bayerl, T., Richter, D., J.

Phys. II France 2 (1992) 1589-1615; [15] Busch, S., Smuda, C., Pardo, L. C., Unruh, T., J. Am. Chem. Soc. ,

2010, 132 (10), pp.3232-3233; [16] Konig S., Sackmann E., Richter D., Zorn R., Carlile C., Bayerl T.

M., J. Chem. Phys. 100 (1994) 3307-3316; [17] Konig, S., Bayerl, T. M., Coddens, G., Richter, D., Sackmann, E.,

Biophys. J. 68 (1995), 1871-1880; [18] Pfeiffer, W., Henkel, T., Sackmann, E., Knoll, W., Richter, D.,

Europhys. Lett., 8 (2), pp. 201-206 (1989).


109

ULTRAFAST OPTICAL CONTROL OF LIGHT-MATTER INTERACTION AND OF WAVE-PARTICLE DUALITY

Rocco Vilardia,*, Salvatore Savastaa

a ) Dipartimento di Fisica della Materia e Ingegneria Elettronica, Università di Messina, I-98166 Messina, Italy * Corresponding author, e-mail: [email protected]

Abstract A recent article [1] theoretically demonstrated the

possibility of an ultrafast control of the wave-particle duality. It exploits a three-level quantum system strongly coupled to a resonant microcavity. The proposed ultrafast optical control can be experimentally realized availing oneself of many different quantum systems ranging from Cooper pair boxes to intersubband polaritons, from semiconductor quantum dots to atomic physics. By sending an opportune sequence of external probe and control pulses it is shown that it is possible to induce a fast coherence sudden death but also it‘s a coherence sudden birth.

Here we theoretically study that process in deeper detail demonstrating that the lost first order coherence is transferred to higher order coherences. Thanks to this process it is, therefore, possible to successively recover first order coherence.

We also discuss a new homodyne-like scheme which exploits phase-locked probe pulses in order to experimentally study the wave-particle duality of the considered quantum system and wave particle duality is easily probed just revealing the photons escaping the microcavity.

Introduction The principal aim of quantum information science and

technology is the control over the modalities of interaction between single photons and individual quantum emitters [2-4]. Thanks to the usage of microcavities, under opportune experimental conditions the strength of the interaction between the quantum emitter and the electromagnetic interaction cavity field can be so intense that light quanta can be absorbed and reemitted many times before escaping the cavity [2,5-9]. In such cases the physical system enters strong coupling regime under which hybrid light-matter quasiparticles arise.

Nowadays strong coupling can be achieved and exploited in many experimental physical system ranging from circuit QED [10,11] to atomic systems [12], from quantum dots [13] in optical microcavities to microcavity embedded quantum wells [14]. Moreover, recent studies show the possibility to achieve the so called ultra strong coupling regime. For all these systems, it is important to be able to switch to and from weak coupling regime and to be able to control the time evolution of coherences.

A recent article points out the possibility to ultrafast switch on and off the strong coupling regime depending on the order and on the particular times at which pulses are sent [1]. In particular it is demonstrated that not only some internal degrees of freedoms can be in strong coupling while others are in weak coupling regime but the same degree of freedom can show a mix of both weak coupling and strong coupling features. Another important achievement of such an article is the demonstration of an ultrafast technique for erasing the first order photonic coherence explaining such a phenomenology in terms of the fundamental quantum complementarity principle directly connected to the information one can achieve about the quantum physical system.

In such an article it is studied the same quantum system discuss in [1]: a single-mode microcavity containing a quantum emitter modeled as a three level fermionic system. The center of the presented research is the study of the modalities of exchange of information between different internal degrees of freedom of the same quantum system and the study of a particular way for controlling and testing the wave-particle duality.

In order to conduct our studies we availed ourselves of computational simulations and of a analytical calculations.

Theoretical model The point of reference of our theoretical study is the

master equation for the density operator

[ , ]i H L (1) where the total Hamiltonian H is

0 I inH H H H (2) being

†0 ,

,1,2j j j a

j gH a a (3)

†

1,2 . .IH g a H c (4) and

* *,1( ) ( ) . .in p c gH t a t H c (5)


110

a and , respectively are the

destruction operator for the single cavity mode and the transition operator of the levels of a quantum emitter.

( )p t represents a Gaussian coherent probe pulses

resonant both with the g e transition and with the

single cavity mode. ( )c t is a control pulse resonant

with the s g transition (see the schemes in figure 1)

The realized computational simulations the adopted parameters are: light-matter coupling constant

85g eV , cavity damping 20a eV , damping

of the ―g‖ level 2g eV , damping of the ―e‖ level

5e meV , pure dephasing of the ―g‖ level

0dg eV , pure dephasing of the ―e‖ level

0de eV , 2 2.28e g meV .

Figure 1 left: The quantum emitter is theoretically represented by the following three level scheme. The fundamental quantum state is s . The first

and the second excited states respectively are g

and e : they respectively are the ground state and the first excited state of the g e transition energetically and strongly coupled to the probe

pulse. On the other hand, the s g transition is energetically resonant with the control pulse.

Figure 1 right: Microcavity scheme. The quantum emitter (green sphere) is placed within the

microcavity which can be externally pumped with probe and control pulses.

Transfer of coherence In order to study the temporal evolution of the general

quantum state we imposed that the initial quantum state is 0 s : the microcavity is empty while the quantum

emitter is in its fundamental state. A probe pulse is sent to the microcavity. Because it is energetically resonant with the single cavity mode, the cavity photon population abruptly reaches a maximum after which it monotonically decays due to cavity losses. A control pulse is sent in correspondence to the second successive minimum.

Because it is energetically resonant with the s g transition, its arrival determines the complete population of the ―g‖ level. Because of the fact that g e transition is energetically resonant and strongly coupled to the single cavity mode than the cavity photon population

†a a shows characteristic vacuum Rabi oscillations

which are also showed by the squared modulus of its

coherent part 2

a . By sending another identical

control pulse in correspondence to a minimum of †a a ,

†a a continues to perform its oscillations while 2

a

vanishes. As explained in [1] such behaviour is explainable thanks to the fundamental quantum complementarity principle (see figure 2).

Figure 2: (Panel a) After the first control pulse

both the cavity photon population †a a (black

dotted line) and the squared modulus of its

coherent part 2

a (continuous red line)

immediately raise for then monotonically decays due to cavity losses. After the first control pulse

strong coupling starts and both begin to oscillate. Cavity photon population continues to oscillate

also after a second control pulse sent in correspondence to a minimum. On the other hand,

2a vanishes. (Panel b) Where

2a vanishes

2

sga oscillates. Before the second control

pulse such coherence was zero but for a short time in correspondence to the arrival of the first control

pulse.

The zeroing of the 2

a poses a natural question.

Where does the information relative to the first order


111

photonic coherence go? Is it lost? Is it transferred? And whereto? For trying to investigate such problematic, it is useful to send a third identical control pulse in

correspondence to a minimum of †a a . The cavity

photon population continues to exhibit vacuum Rabi

oscillations while the 2

a shows a sudden rebirth and

begins to oscillate too. Such phenomenology clearly highlights the fact that the lost-and-then-found first order coherence is transferred to other internal degrees of freedom. The question is now: ―Where is it transferred?‖

A detailed analysis of higher order coherences allows to find the answer. There exist a coherence which is zero before the arrival of the second control pulse and after the third (it is not zero for a small time in correspondence to the first control pulse) and which oscillates between the second and the third control pulse. Such coherence is

2

sga . The amplitude of its oscillation is exactly that

2a would have showed if it would have not suddenly

died due to the arrival of the second control pulse.

This analysis leads to the conclusion that 2

a and 2

sga exchange their behaviour. In other words, the

information relative to 2

a is transferred to other

internal degrees of freedom (see figure 3).

Figure 3: If a third control pulse is sent in correspondence to the minimum of the cavity photon population then †a a continues to

oscillate while 2

a shows a sudden rebirth and 2

sga suddenly dies.

The transfer of coherence is a general mechanism. Sending, for example, the third control pulse in

correspondence to maximum of the cavity photon

population, †a a begins to monotonically decay and 2

a remains zero. In this case, the coherence is

transferred to 2

sga before the first control pulse

while, after it, it is transferred to 2

sga which exhibit

a monotonic decay. Such a behaviour is really important because it testifies that the transfer of coherence takes into consideration the effects of the modifications induced by external pulses (see figure 4).

Figure 4: If the third control pulse is sent in correspondence to the maximum of the cavity photon population then †a a monotonically

decays, 2

a continues to be zero, 2

sga

oscillates between the second and the third control

pulse and the 2

sga monotonically decays

after the third control pulse.

Homodyne test of wave-particle duality a is not a physical observable. For this reason, in

order to study such property we need indirect measurement. To this end, it is possible to exploit an homodyne technique by which ultrafast testing the wave-particle duality exploring an additional degree of freedom: a relative phase between two phase-locked probe pulses sent after an initial control pulse [14,15].


112

212

222

( )( ) exp( ) exp2

( )exp[ ]exp2

P at tt A i t

t tB i

(6)

After a control pulse and a successive first probe pulse at 2 0.14at , the cavity photon population rapidly raises and soon after beginning to oscillate. If a second probe pulse is sent in correspondence to a maximum of †a a at 2 0.88at with a relative

phase 0 destructive interference is observed. If, instead, the relative phase is constructive interference is observed. If between the two phase-locked probe pulses it is sent a control pulse then no interference is observable (see figure 5).

Figure 5:A control pulse is followed by two phase-locked probe pulse. After a second probe pulse sent with a relative phase 0 , destructive

interference is observed. If the relative phase is then constructive interference is obtained. If

between the two phase-locked probe pulse it is sent a control pulse then no interference is

observed.

In other words, thanks to homodyne-like measurement we can access to information relative to inference also in a physical observable which intensity is. After having observed what happens in three specific cases in which it was imposed that the relative phase is either zero or , we studied the phenomenology with a continuous variation of the relative phase (see figure 6 and 7).

Figure 6: (Left) The probe pulse is sent at the first

cavity photon population maximum and intereference is seen in the degree of freedom.

(Right)The same happens if the second probe pulse is sent at the second cavity photon

population maximum. but for a phase with respect to that showed in figure 6 left and in

agreement with [16].

The three three-dimensional figures thus obtained clearly testify the presence or absence of interference in the degree of freedom.

Figure 7: No interference is observed if a control pulse is sent betweeen a the two probe pulses.

If the second control pulse is sent in correspondence to a cavity population maximum then 0ec t

2 2( ) 1 0gt c t g d t s (7) The temporal evolution operator †

pU b a1 is such that the general quantum state after the first three pulses is

2

( ) 1 0

1 0

g

t

p e

t c t g d t s

d t b e s c t e (8)

Noticing that ip pb b e it follows that the

information relative to the phase degree of freedom is

connected only to the coefficient 1 s . If the quantum emitter is in its ―g‖ state then light is connected to the first


113

probe puse. If the quantum emitter is in the ―e‖ level than the light is connected to the second probe pulse. In other terms, monitoring the state of the quantum emitter we acquire the which-way information about the origin of the photon and, therefore, due to fundamental quantum complementarity principle, interference disappears. On the contrary, if the second control pulse is not sent than it is not possible to get such information and, therefore, interference manifests itsself.

Conclusions The presented researches explains the reason why

sudden death and sudden ribirth of coherence happen highlighting that the information relative to a coherence can be transferred to other internal degrees of freedoms of the considered physical system. Such achivement is connected to the possibility to experimentally control in an ultrafast way the trasfer of information within a certain physical system thus paving the way to technological quantum information advancements.

At the meanwhile, these studies explain the way to ultrafast ontrol wave-particle duality thanks to a homodyne-like detection scheme. The studied scheme could find easy experimental realization thanks to its simplicity.

References [1] A. Ridolfo, R. Vilardi, O. Di Stefano, S. Portolan, and S. Savasta,

Phys. Rev. Lett. 106, 013601 (2011); [2] J. M. Raimond, M. Brune, S. Haroche, Rev. Mod. Phys. 73, 565

(2001); [3] C. Monroe, Nature (London) 416, 238 (2002); [4] L. M. Duan and H. J. Kimble, Phys. Rev. Lett. 92, 127902 (2004); [5] C. Weisbuch, M. Nishioka, A. Ishikawa, and Y. Arakawa, Phys.

Rev. Lett. 69, 3314 (1992); [6] J. P. Reithmaier, G. Sek, A. Löffler, C. Hofmann, S. Kuhn, S.

Reitzenstein, L. V. Keldysh, V. D. Kulakovskii, T. L. Reinecke, and A. Forchel, Nature (London) 432, 197 (2004);

[7] T. Yoshie , A. Scherer, J. Hendrickson, G. Khitrova, H. M. Gibbs, G. Rupper, C. Ell, O. B. Shchekin, and D. G. Deppe, Nature (London) 432, 200 (2004);

[8] K. Hennessy, A. Badolato, M. Winger, D. Gerace, M. Atatüre, S. Gulde, S. Fält, E. L. Hu, and A. Imamoglu, Nature 445, 896 (2007);

[9] I. Chiorescu, P. Bertet, K. Semba, Y. Nakamura, C. J. P. M. Harmans, and J. E. Mooij, Nature (London) 431, 159 (2004);

[10] A. A. Abdumalikov, O. Astafiev, A. M. Zagoskin, Yu. A. Pashkin, Y. Nakamura, and J. S. Tsai, Phys. Rev. Lett. 104, 193601 (2010);

[11] B. Peropadre, P. Forn-Diaz, E. Solano, and J. J. Garcia-Ripoll, Phys. Rev. Lett. 105, 023601 (2010);

[12] J. McKeever, A. Boca, A. D. Boozer, J. R. Buck, and H. J. Kimble, Nature 425, 268, (2003);

[13] A. Dousse, Jan Suffczyński, , A. Beveratos, O. Krebs, A. Lemaître, I. Sagnes, J. Bloch, P. Voisin and P. Senellart, Nature (London) 466, 217, (2010);

[14] O. Di Stefano, A. Ridolfo, S. Portolan, and S. Savasta, Opt. Lett. 36 No.22, (2011);

[15] R Vilardi, A. Ridolfo, S. Portolan, S. Savasta, O. Di Stefano, Quantum Complementarity of Cavity Photons Coupled to a Three-Level System, to be published by Physical Review A.;

[16] O. Di Stefano, R. Stassi, A. Ridolfo, S. Patanè, and S. Savasta, Phys. Rev. B, 84, 085324 (2011).


114


115

SEMINARI (Invited)

DEL DOTTORATO DI RICERCA

IN FISICA

Effettuati nel 2011


116

Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 19 Gennaio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica V.le F. Stagno d‘Alcontes 31, Messina Prof. Józef SURA Heavy Ion Laboratory (HIL), University of Warsaw, Poland Seminar title: The HIL Cyclotron and associated ion optics Abstract The isochronous cyclotron of the Heavy Ion Laboratory of Warsaw accelerates ions with mass to charge ratio in the range of A/Q=(2-6) and energies up to 30 MeV per nucleon. The design of this setup includes many of the accelerator physics and ion optics elements.

These elements beginning with the ECR ion source, injection, acceleration, extraction, beam lines, till the experimental setups will be discussed.

________

Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 7 Febbraio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica V.le F. Stagno d‘Alcontes 31, Messina Dr. Ernesto Amato Dipartimento di Scienze Radiologiche, Policlinico dell‘Università di Messina Seminar title: The Geant4 Monte Carlo package from Cern and its applications to nuclear, particle, astroparticle and medical radiation physics Abstract Geant4 (Geometry and Tracking 4) is a Monte Carlo toolkit developed by Cern in object-oriented C++ programming paradigm, for the simulation of nuclear and particle interaction. It offers a wide set of complementary physics models, based either on theory or on experimental data and parametrizations, for electromagnetic and hadronic interactions in energy ranges spanning from some tens of eV to TeV, together with models for nuclear excitation, fission and decay. Extensions to low energy interactions and also to optical photon propagation are available. Complex geometries can be defined and managed, made from elements or compounds whose properties can be obtained from databases or user defined. Volumes can be made ―sensitive‖ to simulate detectors, through the use of hits and digitisation classes. Primary particles propagate through the defined geometry according to the tracking and stepping rules, obeying to the physics models adopted and to the selected cuts. Interaction tracks and cascades can be visualized either online or offline, and relevant quantities are scored in 1-2-3D histograms and n-tuples. Several ancillary softwares from Cern and from application developer teams aid the user in the I/O phases.

After a general introduction to the Geant4 concept, architecture and physical models, I will comment on the different fields of application, spanning from the high energy physics and astrophysics experiments, to the application of radiation physics for dosimetry and radioprotection from sources of photons, leptons and hadrons.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 22 Febbraio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Prof. C.A. Squeri, Prof. V. Candela, Dott. J. Trombetta, Dott. A. M. Roszkowska Ophthalmology Unit, Department of Surgical Specialties, University Hospital of Messina, Messina, Italy. Seminar title: “Clinical applications of the different laser platforms in ophthalmology” Abstract: The purpose of this seminary is to present the clinical applications of the different lasers in ophthalmology. The following lasers will be presented: Femtosecond lasers. This kind of lasers is characterized by ultrashort pulses. They perform horizontal or vertical corneal cuts and are used in corneal and refractive surgery. They are adopted in corneal lamellar keratoplasty and in refractive surgery. Excimer laser and solid state laser. The characteristics of these lasers are used to modify the anterior corneal shape. Flattening or steppening of the corneal surface permit to correct existing refractive errors, so such lasers are widely used in corneal refractive surgery. Argon laser and diode laser These lasers perform retinal photocoagulation. They create retinal scars with effect on retinal pathologies such as diabetic retinopathy, retinal ruptures or holes and degenerations. NdYAG laser.

It is above all a disruptive laser used to treat secondary cataract performing posterior capsulotomy. It is also adopted to resolve an angle closure glaucoma by localized iridotomy (puncture-like openings through the iris without the removal of iris tissue).

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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 4 Marzo 2011, ore 10.00, Conference Room CNR-IPCF V.le F. Stagno d‘Alcontres 37, S. Agata, Messina Seminar title: Ettore Majorana and the Birth of Autoionization Ennio Arimondo Dipartimento di Fisica “E. Fermi”, Università di Pisa Abstract: In some of the first applications of modern quantum mechanics to the spectroscopy of many-electron atoms, Ettore Majorana in 1931 solved several outstanding problems by developing the theory of autoionization. Later literature makes only sporadic references to this accomplishment. After reviewing his work in its contemporary context, we describe subsequent developments in understanding the spectra treated by Majorana, and extensions of his theory to other areas of physics. We find several puzzles concerning the treatment of Majorana's work in the subsequent literature and the way in which the modern theory of autoionization was developed. The relevant papers are those numbered 3 and 5 in the convenient collection, Ettore Majorana Scientific Papers: On the occasion of the centenary of his birth, ed. G. F. Bassani et al. (SIF, Bologna 2006), where they are accompanied by English translations and commentary. The originals are, respectively, ``I presunti termini anomali dell'elio,"E. Majorana, Il Nuovo Cimento, 8, 78 (1931) and ``Teoria dei tripletti P' incompleti," E. Majorana, Il Nuovo Cimento, 8, 107 (1931).


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 24 marzo, alle ore 15.00 nella sala conferenze del CNR di Messina V.le F. Stagno d‘Alcontres 37, S. Agata, Messina Seminar Title: Optical Properties of Carbon-based Materials Elefterios Lidorikis Department of Materials Science & Engineering, University of Ioannina, Ioannina GR-45110 Greece Abstract: Carbon nanotubes (CNTs), and more recently graphene, have been at the center of nanotechology research, with the search for new technologies based on their mechanical and electrical properties ever increasing. Graphene, a two-dimensional honeycomb lattice of carbon atoms, can be thought of as the ―building block‖ of other carbon allotropes: it can be ―wrapped‖ into fullerenes, ―rolled‖ into CNTs or ―stacked up‖ into graphite, with many of their properties deriving from graphene. In this presentation we discuss different aspects of the photonic response of graphene and CNTs. After a brief introduction to the basic electronic structure and optical properties of graphene, we discuss recent advances in understanding interference-enhanced (IERS) and surface-enhanced Raman scattering (SERS) phenomena in graphene. Especially in terms of SERS, graphene provides the ideal prototype two-dimensional test-material for its investigation. We discuss recent SERS experiments on graphene and develop a quantitative analytical and numerical theory for its description. Next, we investigate the photonic properties of two-dimensional CNT arrays for photon energies up to 40eV and unveil the physics of two distinct applications: deep-UV photonic crystals and total visible absorbers. We find three main regimes: for small intertube spacing of 20-30nm, we obtain strong Bragg scattering and photonic band gaps in the deep-UV range of 25~35 eV. For intermediate spacing of 40-100nm, the photonic bands anti-cross with the graphite plasmon bands resulting into a complex photonic structure, and a generally reduced Bragg scattering. For large spacing >150nm, the Bragg gap moves into the visible and decreases due to absorption. This leads to nanotube arrays behaving as total optical absorbers. These results can guide the design of CNT-based photonic applications in the visible and deep UV ranges. ________ Dottorato di Ricerca in Fisica, Università di Messina Avviso di Seminario 30 Marzo 2010, Ore 15.00, aula E. Majorana, Dipartimento di Fisica, Università di Messina, V.le F. Stagno D‘Alcontres 31, S. Agata, Messina Prof. Avazbek NASIROV Bogoliubov Laboratory of Theoretical Physics of the Joint Institute for Nuclear Research of Dubna (Russia) Seminar title: "The role of the entrance channel in study of fusion-fission reaction mechanisms " Abstract: Evaporation residues and binary fragments are main products of the heavy ion collisions at beam energies around the Coulomb barrier. The new superheavy elements Z=110-118 are the evaporation residues after emission of neutrons from the heated compound nucleus which is formed in the complete fusion of projectile and target nuclei. Due to very small cross section of the synthesis of superheavy elements it is convenient to study the reaction mechanism by the analysis of fusion-fission fragments formed at fission of compound nucleus. But the fusion-fission fragments are mixed with the quasifission and fast fission fragments which are formed without formation of compound nucleus. In this seminar we will discuss the mechanisms and contributions of these three fissionlike processes to help experimentalists at the choice of reactions for the synthesis of new superheavy elements.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 14 Aprile 2011, ore 15.00, Aula E. Majorana, Dipartimento di Fisica V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: Nuclear Energy: how does it work? Dr.ssa Marina Trimarchi Dipartimento di Fisica, Università di Messina Abstract: The possibility to produce energy from nuclear transmutations is a consequence of the Einstein‘s equation, stating the equivalence between mass and energy. Fission reactions represent a very powerful energy source, showing a yield 2 millions higher than that of fossil fuels, without greenhouse gases emission. Nuclear power plants working principles will be illustrated, with particular attention to safety aspects, in operational mode as well as in case of accident. In particular, differences between various generations reactors will be stressed, starting from old RMBK type (Chernobyl) to the newest EPR type. Other correlated aspects, as nuclear waste disposal and non-proliferation of nuclear weapons will be considered. Finally, due to recent event regarding Fukushima nuclear accident, an overview of the actual nuclear risk and its consequences worldwide will be given.

________ Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 5 Maggio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Dr.ssa Valentina Venuti Dipartimento di Fisica, Universita’ di Messina, CNISM, UdR Messina, Viale Ferdinando Stagno D’Alcontres 31, P.O. BOX 55, 98166 Messina, ITALY. Email: [email protected] Seminar title: Vibrational dynamics and chiral recognition in Ibuprofen/ -cyclodextrins inclusion complexes: FTIR-ATR and numerical simulation results Abstract Cyclodextrins are supramolecular host systems able to encapsulate molecules in their hydrophobic cavity via noncovalent interactions. Their chiral recognition properties, not fully characterized yet, are of great relevance in pharmaceutical industry.

Here, we studied how the vibrational properties are affected by the chiral recognition process, upon selection of the non-steroidal anti-inflammatory drug Ibuprofen (IBP) in its chiral (R)- and (S)-, and racemic (R, S)- forms, as model guest, and native and modified -cyclodextrins ( -CDs) as model host. The changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, have been studied, in solid phase, by attenuated total reflection Fourier transform infrared FTIR-ATR. The recorded spectra have been compared with the wavenumbers and IR intensities as obtained by simulation for the free and complexed guest molecule. By the temperature-dependent analysis of the vibrational spectra in the C=O stretching region, the complexation mechanism has been discussed. It turned out to be enthalpy-driven, with enantiomers of IBP giving rise to more stable inclusion complexes with respect to the racemate. This combined experimental-numerical approach gave crucial information on the expected different ―host-guest‖ interactions that drive the chiral recognition process, helpful to put into evidence differences in the conformational properties of the complexes, that are retained a prerequisite for chiral recognition.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 14 Giugno 2011, ore 12.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Dr.ssa Mariapompea Cutroneo Dottorato di Ricerca in Fisica, Università di Messina Seminar title: “High Energy proton/ion beams production by sub-ns, kJ-laser plasma interaction” Abstract The purpose of this seminar is to present some preliminary results recently obtained in the European & International Experiment, directed by Prof. L. Torrisi of Messina University, at the PALS Laboratory of Prague (Czech Republic), under the support given by LASERLAB Europe. Particularly will be presented some preliminary results concerning the plasma generation in forward direction through thin laser irradiated targets, the plasma laser acceleration of protons and ions at energies above 1 MeV, the new detection technique employing Thomson parabola and semiconductor SiC detectors in time-of-flight configuration, and the first measurements of D-D nuclear fusion induced by 4 MeV deutons accelerated by the laser-plasma.

The original results and experimental approaches will be discussed in view of a more details descriptions that will be given in the specific scientific Journals.

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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 21 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: Electron correlations in metals: Dynamical mean-field theory Václav Janiš Institute of Physics, Academy of Sciences of the Czech Republic,Prague

Abstract

Electrons in metals feel only a screened, short-range Coulomb repulsion. In most of the transition metals, lanthanides and actinides electron correlations are not negligible. To describe the correlation effects correctly one needs a reliable description of strong electron correlations. Gross features of weak excitations of the ground state of interacting fermions are described by Fermi-liquid theory. To assess collective phenomena with quantum coherence in heavy metals, it is necessary to go beyond the framework of Fermi liquid. The way to go systematically beyond Fermi-liquid theory is offered by the so-called Dynamical Mean-Field Theory. We review in this talk the underlying ideas of the dynamical mean-field theory originating in the single-impurity Anderson model and the Kondo effect. We further discuss various aspects of presently the most advanced theory of strongly correlated electrons with examples of its application in model and realistic calculations of electronic properties of metals.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 23 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: Electrical conductivity and charge diffusion in disordered solids Václav Janiš Institute of Physics, Academy of Sciences of the Czech Republic,Prague

Abstract: Electrical resistivity (Ohm‘s law) in solids is caused by the scattering of almost free conduction

electrons on impurities and irregularities in the periodic lattice. The basic theoretical tools for description of quantum transport are linear response theory and Kubo formulas. We review in this talk many-body and Green function methods of calculation of the impact of scatterings of electrons on randomly distributed impurities in metals. We stress the necessity of renormalizations of the perturbation expansion in the strength of the impurity potential and of consistency between one- and two-electron Green functions dictated by conservation laws, electron-hole symmetry and and gauge invariance of the electromagnetic system. Finally we discuss disorder-driven metal-insulator transitions due to discharging of the Fermi energy and due to vanishing of diffusion in the limit of strong randomness.

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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 28 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: Il contributo Light-by-Light al momento magnetico anomalo del muone. Stato attuale e prospettive future. D. Moricciani

INFN, Sezione di Roma \Tor Vergata", I-00133 Roma, Italy


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 7 Luglio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: MESON PHOTOPRODUCTION AT GRAAL AND MAMBO Dott.ssa R. Di Salvo INFN Sezione di Roma Tor Vergata Abstract

Meson photoproduction on the nucleon is a powerful tool for the understanding of the nucleon structure and of the baryon resonances involved in the reaction process. Polarized photon beams, in combination with large solid angle apparata and/or high precision spectrometers, allow to access polarization observables, which are particularly sensitive to the properties of baryon resonances, such as parity and spin. Some of the main results of the GRAAL experiment in Grenoble and the future plans for the MAMBO experiment, which is presently under construction in Bonn, will be shown and discussed in detail.

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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 11 Luglio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: Thomson parabola spectrograph in investigations of MeV energy ions from laser plasma ion sources Andriy Velyhan Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic

Abstract Laser ion sources (LIS) already have found a wide applications in areas such as material modification,

ion implantation, pulsed laser deposition. LIS can deliver ions with ionization states from Z= 1 up to 55, and energies ranges from hundreds of eV up to several MeV. Investigations of the interaction of laser radiation with solid targets is possible by using of Thomson parabola spectrograph (TPS). The operation principle of the TPS is based on the gradual passage of ions through parallel electric and magnetic fields. It is an excellent device, which is capable to give a general overview of the charge states and of the velocity (kinetic energy) distributions of all type of ions produced in a single laser shot only.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 28 Settembre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. S. d‘Alcontres 31, S. Agata, Messina; Seminar title: “Laser-generated plasma and its applications”; Dr. Francesco Caridi, Physics Ph.D. ; Facoltà di Scienze MM. FF. NN., Univ. di Messina, Viale F. S. d’Alcontres, 31 – 98166 – Messina, Italy ;INFN-Sez. CT, Gr. Coll. di Messina, Viale F. S. d’Alcontres, 31 – 98166 – Messina Plasma production by laser ablation (PLA) of solid targets in vacuum is a topic of growing interest for many applications in different fields, such as diagnostics techniques, ion acceleration, nuclear physics, material processing and cultural heritage. Key plasma parameters, such as equivalent temperature, density, acceleration voltage, ion charge state and fractional ionization, are evaluated using appropriate diagnostics instruments, such as ion collector, ion energy analyzer, mass quadrupole spectrometer, optical spectroscope. These tools give us essential information to understand the mechanism of non-equilibrium plasma development and kinetics. A special interest of PLA concerns the ion acceleration with high-electrical fields generated in sub-millimeter space by hot and dense laser-generated non equilibrium plasmas. This new method of producing ion beams is more appealing than classical techniques that use large accelerator facilities, and, recently, it has been investigated in order to develop a new generation of laser ion sources (LIS). Furthermore, when extremely intense laser beams interact with deuterated targets, D-D nuclear fusion reactions can be achieved in hot and dense plasmas. Many laboratories are using PLA in order to grow thin films as coverage of different substrates. The film properties, such as stoichiometry, roughness, grain size, crystallinity and porosity, can be modified on the basis of the used laser wavelength, pulse intensity, pulse width, substrate nature, irradiation environment conditions, etc. The technique is useful in many scientific fields, such as microelectronics, chemistry, biomedicine and metallurgy. Laser Ablation coupled to Mass Quadrupole Spectrometry (LAMQS) is a new technology recently developed for the depth profile and compositional analysis of different solid materials placed in vacuum. It is very helpful in the field of cultural heritage in order to compare their composition and morphology and to identify their origin and the type of manufacture.

________ Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 18 Ottobre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. S. d‘Alcontres 31, S. Agata, Messina; Seminar title: Electroencephalographic signal processing: the use of Independent Component Analysis and its application to complex motor task. Dr.ssa Simona Lanzafame University of Messina, Department of Matter Physics and Electronic Engineering. The City College of New York, CUNY, Sophie Davis School of Medicine. Electroencephalographic (EEG) signal obtained from scalp electrodes is a sum of the large number of neurons potentials. The interest of the scientific community is in studying the potentials in the sources inside the brain and not only the potentials on the scalp, which globally describe the brain activity. The recovery of the exact cortical distribution of an EEG source region is limited by the unsolved of the inverse source localization problem. For example, far-field potentials from two synchronously active but physically opposing cortical source areas – e.g., source areas facing each other on opposite sides of a cortical sulcus – may cancel and their joint activity will have no effect on the scalp data. An ideal goal for EEG analysis should be to detect and separate activities in multiple concurrently active EEG source areas, regardless of their relative straights at different moments. A new approach to finding EEG source activities has been developed based in a simple physiological assumption that across sufficient time, the EEG signals arising in different cortical source domains are temporally independent of each other. This means that measuring the scalp EEG activity produced in some of the source domains at a given moment allows no inferences about EEG activities in the other source domains at the same instant. This insight and the resulting algorithms for signal separation that have emerged in the last decade have created a new field within signal processing in general, known in particular as independent component analysis (ICA). We will discuss the important findings obtained by a novel application of the ICA algorithm to complex motor task.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 14 Novembre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. S. d‘Alcontres 31, S. Agata, Messina; Seminar title: Fukushima: Eight months after ; Dr.ssa Marina Trimarchi Dipartimento di Fisica, Università di Messina e INFN – Gruppo Collegato di Messina Abstract The accident occurred at the Fukushima Daichi NPP as a consequence of the Japan Earthquake and Tsunami, classified at 6th level of the INES, has involved a significant release of radioactive materials, inducing a considerable contamination and irradiation risk to people and environment. Actually the short term consequences typical of a nuclear accident can be considered quite overcome, although the recovery process of the reactors of Fukushima Daichi NPP is a slow and difficult process, still requiring continuous and arduous efforts from TEPCO workers and Japanese volunteers. For what concerns the long term risks due to this nuclear accident, a comprehensive understanding of the contamination status of the environment is necessary to choose the suitable countermeasures to adopt. In this framework, Japanese government is still providing an astonishing effort in evaluating contamination and exposure data, that are continuously and correctly shared not only with the scientific and government institutions involved, but also with the public. A survey of the reactor status, and of the actual contamination and exposure levels will be provided, together with a description of the remediation activities and countermeasures adopted from the government institution, in the framework of the international recommendations. Finally, the lesson learned from the Fukushima accident will be discussed, and a short comparison with the Chernobyl experience will be attempted, to better understand risks and consequences of a nuclear accident in the third millennium scenario.

________ Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 21 Novembre 2011, ore 15.00, Sala Seminari IPCF-CNR, V.le F. S. d‘Alcontres 37, S. Agata, Messina Seminar title: Salty ice under pressure; Dr. Antonio Marco Saitta Physique des Milieux Denses, IMPMC, CNRS-UMR 7590, Université Pierre et Marie Curie, Paris Abstract Water, wherever it exists in nature, contains unavoidably significant amounts of dissolved ionic species. Nonetheless, surprisingly little experimental attention has been paid on the high pressure behaviour of ―salt water‖ compared to pure water. In a recent study combining neutron diffraction and molecular dynamics simulations we showed the existence [3] of a polyamorphic transition in LiCl:6D2O between a high-density (HDA) and a very-high-density amorphous (VHDA) form. In spite of the high amount of salt, LiCl:6D2O vitrifies at ambient pressure in a structurally compact form very similar to the relaxed high-density amorphous phase of pure water (e-HDA) [1]. We show that the transition to salty-VHDA takes place abruptly at 120 K and 2 GPa under annealing at high pressure, is reversible. We suggest that the transition is linked to a local structural reorganization of water molecules around the Li ions. The possible connection of this transition with the analogous observed [1] in pure water and the generality of the occurrence of a polyamorphism phenomenon in solutions in which one component, water, can have two critical points [2] will be discussed. Under further annealing at high pressure (~4GPa), the salty-VHDA amorphous crystallizes, for a temperature of ~270 K, in a new and unexpectedly simple salt hydrate [4], which can be regarded as an ―alloyed‖ high-pressure ice phase. Such ―salty‖ ice VII has significantly different structural properties compared to pure ice VII, such as a 8% larger unit cell volume, 5 times larger displacement factors, frozen rotational disorder, absence of transition to an ordered ice VIII structure, and most likely ionic conductivity. Our study strongly suggests that there is a whole new class of salt hydrates based on various kinds of solutes and high pressure ice forms. If these exist in nature in significant quantity, their physical properties would be highly relevant for the understanding of icy bodies in the solar system. [1] R. J. Nelmes et al., Nature Phys. 2 414, (2006). [2] P. G. Debenedetti and H. E. Stanley, Phys. Today 40 (2003). [3] L. E. Bove, S. Klotz, J. Philippe, and A. M. Saitta, Phys. Rev. Lett. 106, 125701 (2011). [4] S. Klotz, L. E. Bove, T. Strassle, T. C. Hansen, and A. M. Saitta, Nature Materials 8, 405 (2009)


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 1 Dicembre 2011, ore 15.00, Sala Seminari IPCF-CNR V.le F. Stagno d‘Alcontres 37, S. Agata, Messina Seminar title: A novel hybrid top-down/bottom-up approach for nanoparticle synthesis: Laser ablation in reversed micellar solution Dr. Pietro Calandra IPCF-CNR Sede di Messina If the building up of smaller and smaller structures promptly answers the recent technological request of more and more miniaturized devices, it is also true that new and exotic features arise below a certain size threshold of particles basically due to quantum confinement of charge carriers (Quantum Size effects). In addition to size effects, further peculiar properties are expected to arise by controlling the spatial location of different materials, e.g. semiconductor and metal domains, within each nanoparticle [1]. In fact, it is well known that semiconductor/metal junctions give rise to very interesting phenomena which have been exploited in a wide range of technological applications (transistors, rectificator junctions, Ohmic contacts as well as effective photocatalysts). In order to prepare A@B-type materials (A and B referring to two different materials), we set up a novel synthetic method based on the laser ablation of a target of the material A, immersed in a reversed micellar solution containing nanoparticles of the material B. This strategy is a winning example of an hybrid approach combining, in a synergistic way, the advantages of a top-down approach (high purity of the ablated particles [2]) and a bottom-up one (synthesis of B and self-assembly of A onto it). [1] T. Hirakawa and P. V. Kamat, J. Am. Chem. Soc. 127, 3928 (2005). [2] P. Calandra et al., Materials Letters 64, 576 (2010).

________

Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 5 Dicembre 2011, ore 15.00, Sala Seminari IPCF-CNR V.le F. Stagno d‘Alcontres 37, S. Agata, Messina Seminar title: Magnetically induced birefringence in magnetic nanoparticles suspensions Dr. Mikolaj Pochylski Division of Optics, Dept. of Physics, Adam Mickiewicz University, Poland Abstract

In this talk the magnetically induced birefringence method will be shown as a method useful in discrimination between different mineral structures and sizes of magnetic nanoparticles. The basic principles of the technique and its simple experimental realization will be explained. The applicability of the method will be presented for several biomedically relevant systems.


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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 20 Dicembre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d‘Alcontres 31, S. Agata, Messina Seminar title: La «particella di Dio» e l'origine della massa Paolo Castorina Dipartimento di Fisica e Astronomia, Universita di Catania Abstract Al Centro Europeo Ricerche Nucleari (CERN) di Ginevra è in funzione la piùgrande macchina che l'uomo abbia mai costruito: il Large Hadron Collider (LHC). Si accelerano e si fanno urtare particelle di energia altissima perverificare le leggi fondamentali della Natura. LHC ci ha già permesso di raggiungere temperature molto simili a quelle dell'inizio del Big Bang cosmologico ed al CERN è stata anche intrappolata l'antimateria. Ma non siè ancora trovata la particella di Higgs la cui esistenza confermerebbe completamente l'attuale teoria unificata delle interazioni elettromagnetiche e deboli e, soprattutto, spiegherebbe l'origine della massa. La massa, anche quella delle particelle più piccole, non è una proprietà fondamentale. Essa deriva dalle forze di interazione e, in particolare, dall'esistenza di una nuova particella, battezzata "particella di Dio", attraverso un affascinante meccanismo, detto rottura spontanea della simmetria, che viene descritto con semplici esempi.

Infine, i recenti risultati preliminari di LHC, presentati al CERN il 12 Dicembre 2011 e riportati dalla stampa internazionale, verranno brevemente discussi.


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Organizzazione

del Dottorato di Ricerca in Fisica

dell‘Università di Messina

Ciclo (XXVI)


128

Organization and Personnel

PhD COORDINATOR : PROF. LORENZO TORRISI

TEACHERS OF REFEREMENT FOR THE DIFFERENT CURRICULA:

PROF. G. CARINI CURRICULUM STRUTTURA DELLA MATERIA PROF. GIORGIO GIARDINA CURRICULUM FISICA NUCLEARE

PROF. PAOLO V. GIAQUINTA CURRICULUM FISICA MAT. SOFF. E DEI SIST. COMPL.

PROF. DOMENICO MAJOLINO CURRICULUM FISICA APPLICATA

DIRECTOR OF PHYSICS DEPARTMENT OF MESSINA UNIVERSITY:

PROF. GIACOMO MAISANO

DIRECTOR OF MATTER PHYSICS AND ELECTRONIC ENGINEERING DEPARTMENT:

PROF. FORTUNATO NERI

SCHOOL MANAGER: DR PAOLA DONATO

ADMINISTRATION PERSONNEL: Mrs. GIUSEPPA LA SPADA

Mrs. ROSANNA ARENA Mrs. GAETANA PANTO’

Mr. SALVATORE RANDO


129

Curriculum di Struttura della Materia (15 moduli/180 ore).

DISCIPLINA MODULI Prof.copertura

Fisica stati

condensati (45)

Fisica dello stato solido (15) Ginatempo Fisica dei solidi amorfi (15) D‘Angelo

Fisica dei liquidi (15) Caccamo

Fisica Teorica (20)

Fisica Relativistica (10) Savasta Teoria dello scattering elettromagnetico (10)

Borghese

Metodi Matematici e computazionali della Fisica (30)

Tecniche di Calcolo della Fisica (10)

Savasta

Fondamenti di informatica e Fisica computaz. (10)

Costa-Ginatempo

Simulazione di sistemi all‘equilibrio (10)

Costa-F.Sajia

Tecniche Spettroscopiche

(40)

Spettr. Neutronica (10) Wanderlingh Spettr. Ottica (10) Majolino

Spettr. Acustica e dielettrica (10)

Mandanici-Tripodo

Spettr. Elettronica (10) Mondio

Fisica Sistemi

Complessi (30)

Fenomenologia dei sistemi complessi (15)

Magazù

Fisica sistemi a molti corpi (15)

Malescio-Prestipino

Fisica Nucleare (15)

Teoria delle interazioni fondamentali (15)

Trifirò


130

Curriculum di Fisica della Materia Soffice e dei Sistemi complessi (15 moduli/180 ore).

DISCIPLINA MODULI Prof.copertura

Fisica degli stati condensati (45)

Fisica dei liquidi (15) Caccamo Fisica dei solidi amorfi (15) D‘Angelo

Sistemi metastabili (15) Giaquinta

Fisica della Materia soffice e dei sistemi

complessi (45)

Colloidi e polimeri e aggregati supramolecolari (20)

Micali

Sistemi di interesse biofisico (15) Magazù Sistemi caotici, finanziari; reti (10) Malescio

Argomenti avanzati di Fisica dei Liquidi (20)

Miscele di liquidi e liquidi carichi (10)

F. Saija

Liquidi a legame idrogeno (10) Mallamace

Tecniche

Spettroscopiche (30)


Spettr. Acustica e dielettrica (10) Mandanici-Tripodo

Metodi Matematici e computazionali della

Fisica (20)

Fondamenti di informatica e Fisica computazionale (10)

Costa-Ginatempo

Simulazione di sistemi all‘equilibrio (10)

Costa-F.Saija

Metodi di

Simulazione Avanzati (20)

Simulazione di sistemi fuori dall‘equilibrio (10)

Prestipino

Metodi numerici per lo studio di transizioni di fase (10)

Prestipino


131

Curriculum di Fisica Applicata ai Beni Culturali (15 moduli/180 ore).

DISCIPLINA MODULI Prof. copertura Fisica stati condensati

(25) Fisica dei solidi amorfi (15) D‘Angelo

Fisica dei Materiali (10) Mondio

Fisica Teorica (10) Teoria dello scattering elettromagnetico (10)

Borghese-Iatì


Fisica (20)


Savasta


Costa-Ginatempo

Tecniche Spettroscopiche (50)

Introduzione alle tecniche spettroscopiche (10)

Crupi


Spettroscopia Acustica e dielettrica (10)

Mandanici-Tripodo

Spettr. Elettronica (10) Mondio

Fisica dei sistemi complessi (30)

Fenomenologia Sistemi complessi (15)

Magazù

Fisica sistemi a molti corpi (15) Malescio-Prestipino

Metodologie Fisiche applicate ai Beni

Culturali (45)

Archeometria (10) Majolino

Metodologie Sperimentali e strumentazione in Fisica applicata

ai Beni Culturali (15)

Torrisi-Magazù

Metodologie nucleari in Fisica Applicata (20)

Barnà-Trifirò-Fazio


132

Curriculum di Fisica Applicata ai Beni Ambientali (15 moduli/180 ore).

DISCIPLINA MODULI Prof. copertura Fisica stati condensati

(30) Fisica dello stato solido (15) Ginatempo Fisica dei solidi amorfi (15) D‘Angelo

Fisica Teorica (10) Teoria dello scattering elettromagnetico (10)

Borghese-Iatì


Fisica (20)


Savasta


Costa-Ginatempo

Tecniche Spettroscopiche (40)

Introduzione alle tecniche spettroscopiche (10)

Crupi


Radioattività e Spettroscopia Gamma (10)

Barnà - Trifirò

Fisica dei sistemi complessi (30)

Fenomenologia Sistemi complessi (15)

Magazù

Fisica sistemi a molti corpi (15) Malescio-Prestipino

Metodologie Fisiche applicate ai Beni Ambientali (50)

Metodologie Sperimentali e strumentazione in Fisica applicata

ai Beni Ambientali (15)

Torrisi-Magazù

Inquinamento Acustico e normativa (15)

Federico

Metodologie nucleari in Fisica Applicata (20)

Barnà-Trifirò-Fazio


133

Curriculum di Fisica Nucleare (13 moduli/180 ore).

DISCIPLINA MODULI Prof. copertura

Fisica Teorica (10) Teoria dello scattering elettromagn.

in processi Nucleari (10) Iatì-Maidaniuk-

Giardina


Teoria delle interaz. Fondam. (15) Trifirò Teoria delle reazioni Nucleari

indotte da ioni leggeri (10) Giardina - Nasirov

Teoria delle reazioni Nucleari indotte da ioni pesanti (20)

Giardina - Nasirov

Spettroscopia Nucleare (20) Barnà

Metodi Matematici e computazionali della Fisica (15)

Acquisizione ed elaborazione dei dati sperimentali (15)

Barnà

Fisica Sistemi

Complessi (30)

Fenomenologia sistemi complessi (15)

Magazù

Fisica dei sistemi a molti corpi (15) Malescio-Prestipino

Apparati di

rivelazione in Fisica Nucleare e subnucleare (30)

Rivelazione dei prodotti di reazione e metodologie di Analisi in


Trifirò

Rivelazione dei prodotti di reazione e metodologie di Analisi in

Fisica subnucleare (15)

Trifirò

Fisica subnucleare (30)

Risonanze barioniche con sonde elettromagnetiche in fisica

relativistica (10)

Di Salvo

Procedure di simulazione nelle reazioni di fotoproduzione di

Mesoni (10)

Moricciani

Astrofisica Nucleare (10) Italiano


134

Collegio dei Docenti del Dottorato di Ricerca in Fisica

Ciclo XXVI

1. Abramo Maria Concetta

2. Barnà Calogero Renato

3. Borghese Ferdinando

4. Branca Caterina

5. Caccamo Carlo

6. Carini Giuseppe

7. Costa Dino

8. Crupi Vincenza

9. Cutroni Maria

10. D‘Angelo Giovanna

11. Di Salvo Rachele Anna

12. Giaquinta Paolo Vittorio

13. Giardina Giorgio

14. Ginatempo Beniamino

15. Gucciardi Pietro

16. Iatì Maria Antonia

17. Magazù Salvatore

18. Maisano Giacomo

19. Majolino Domenico

20. Malescio Gianpietro

21. Mandanici Andrea

22. Maragò Onofrio

23. Micali Norberto

24. Mondio Guglielmo

25. Moricciani Dario

26. Prestipino Giarritta Santi

27. Saija Franz

28. Torrisi Lorenzo

29. Trifirò Antonio

30. Tripodo Gaspare

31. Wanderlingh Ulderico

[email protected];

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135

ELENCO DOTTORANDI DI RICERCA IN FISICA: XXIV CICLO Curriculum D‘ANDREA Cristiano Struttura della Materia [email protected] FINA Natale Struttura della Materia [email protected] RIFICI Simona Struttura della Materia [email protected] SCARDINA Francesco Fisica Nucleare [email protected] TRIMARCHI Antonio Struttura della Materia [email protected] VILARDI Rocco Struttura della Materia [email protected] XXV CICLO CACCIOLA Adriano Struttura della Materia [email protected] DI BARTOLO Federico Fisica Nucleare [email protected] FISICHELLA Maria Fisica Nucleare [email protected] MINNITI Triestino Fisica Nucleare [email protected] ROMANIUK Mariia Fisica Nucleare [email protected] SANTORO Simone Fisica Nucleare [email protected] XXVI CICLO CURCIARELLO Francesca Fisica Nucleare [email protected] CUTRONEO Mariapompea Struttura della Materia [email protected] DE LEO Veronica Fisica Nucleare [email protected] SAYED Rania Strutt. della Materia [email protected] STASSI Roberto Struttura della Materia [email protected]


136

Tesi del Dottorato di Ricerca in Fisica Ciclo XXIV

XXIV CICLO

DOTTORANDO CURRICULUM ARGOMENTO TESI TUTORE / CO-TUTORE

Dott. D‘Andrea Cristiano Struttura della Materia Surface enhanced Raman spectroscopy di proteine Dott. Pietro G.Gucciardi

Prof. Fortunato Neri

Dott. Fina Natale Struttura della Materia Nano-ottica: diffusione ed emissione di luce in

presenza di nanoparticelle metalliche. Prof. Guglielmo Mondio Dott. Salvatore Savasta

Dott.ssa Rifici Simona Struttura della Materia Struttura delle biomembrane investigata tramite la

spettroscopia NMR e la diffrazione di raggi X. Prof. Ulderico Wanderlingh

Dott. Scardina Francesco Fisica Nucleare

Dynamics of the quark-gluon plasma in ultra-relativistic heavy-ion collision. A transport theory

for the interaction between the minijets and the bulk of the plasma.

Prof. Giorgio Giardina Prof. Vincenzo Greco

Dott. Trimarchi Antonio Struttura della Materia

Struttura e dinamica di biomembrane investigate con small angle X-Ray scattering e spettroscopia di

neutroni.

Prof. Ulderico Wanderlingh

Dott. Vilardi Rocco Struttura della Materia Interazione radiazione materia in regime non

perturbativo. Prof. Ezio Bruno

Dott. Salvatore Savasta


137

Pubblicazioni 2011

degli studenti del Dottorato di Ricerca in Fisica

dell’Università di Messina


138

PUBBLICAZIONI 2011 XXIV Ciclo

Cristiano D’Andrea

1. Re-Radiation Enhancement in polarized Surface-Enhanced Resonant Raman Scattering of Randomly Oriented Molecules on Self-Organized Gold Nanowires, B. Fazio, C. D‘Andrea, F. Bonaccorso, A. Irrera, G. Calogero, C. Vasi, P.G. Gucciardi, M. Allegrini, A. Toma, D. Chiappe, C. Martella, and F. Buatier de Mongeot, ACS NANO, Vol 5, No 7 (2011) Pag. 5947-5956;

2. Manipulation and Raman Spectroscopy with Optically Trapped Metal Nanoparticles Obtained by Pulsed Laser Ablation in Liquids, E. Messina, E. Cavallaro, A. Cacciola, R. Saija, F. Borghese, P. Denti, B. Fazio, C. D‘Andrea, P. G. Gucciardi, M. A. Iati, M. Meneghetti, G. Compagnini, V. Amendola, and O.M. Maragò, Journal of Physical Chemistry C 115 Issue 12 (2011) Pag. 5115-5122;

3. SERS activity of pulsed laser ablated silver thin films with controlled nanostructure E. Fazio, F. Neri, C. D‘Andrea, P. M. Ossi, N. Santo and S. Trusso Journal of Raman Spectroscopy 42 (2011) Pag. 1298-1304;

4. Synthesis by pulsed laser ablation in Ar and SERS activity of silver thin films with controlled nanostructure, C. D‘Andrea, F. Neri, P. M. Ossi, N. Santo and S. Trusso, Laser Physics 21 Issue 4 (2011) Pag 818-822.

5. Spectral dependence of the Amplification Factor in SERS (Poster), C. D‘Andrea, B. Fazio, A. Irrera, P. Artoni,

O.M. Maragò, M. A. Iatì, G. Calogero, P. G. Gucciardi, Proceedings International Summer School on ―Plasmonics, Functionalization and Biosensing‖, Kirchhoff Institute for Physics, University of Heidelberg, 24-30 Aprile 2011;

6. Spectral dependence of the Amplification Factor in Surface Enhanced Raman Spectroscopy (Poster), C. D‘Andrea, B. Fazio, A. Irrera, P. Artoni, O.M. Maragò, M. A. Iatì, G. Calogero, P. G. Gucciardi, Proceeedings International Summer School on "NANO-OPTICS: Plasmonics, Photonic Crystals, Metamaterials and Sub-Wavelength Resolution", Ettore Majorana Foundation and Centre for Scientific Culture, Erice (TP), 03-18 Luglio 2011;

7. Spectral dependence of the Amplification Factor in Surface Enhanced Raman Spectroscopy (Poster), C. D‘Andrea, B. Fazio, A. Irrera, P. Artoni, O.M. Maragò, M. A. Iatì, G. Calogero, P. G. Gucciardi, Proceedinggs Electromagnetic and Light Scattering XIII, Conference, Taormina 26-30 Settembre 2011.

Natale Fina

1. A.Ridolfo, N.Fina, O.Di Stefano, O.M. Maragò , S.Savasta. Photoluminescence from a Dimer Nanoantenna:

From Purcell Effect to Nanopolaritons. in Progress on ACS Nano.

Simona Rifici

1. S. Rifici, C. Crupi, G. D‘Angelo, G. Di Marco, G. Sabatino, V. Conti Nibali, A. Trimarchi and U. Wanderlingh, “Effects of a short length alcohol on dimyristoylphosphatidylcholine system”, Philosophical Magazine, 91 2014-2020, (2011);

2. S. Rifici, U. Wanderlingh, G. D‘Angelo, C. Crupi, A. Trimarchi, V. Conti Nibali, “Effects of medium-chain alcohols on the structure of phospholipid bilayers”, Il Nuovo Cimento, in press.


139

Francesco Scardina

1. ―Impact of temperature dependence of the energy loss on jet quenching observables‖ F. Scardina, M. Di Toro, V. Greco. Oct 2011. 7 pp. Published in Nuovo Cim. C34N2 (2011) 67-73

Antonio Trimarchi

1. S. Rifici, C. Crupi, G. D‘Angelo, G. Di Marco, G. Sabatino, V. Conti Nibali, A. Trimarchi and U.

Wanderlingh, ―Effects of a short length alcohol on dimyristoylphosphatidylcholine system‖, Philosophical Magazine, 91 2014-2020, (2011);

2. S. Rifici, U. Wanderlingh, G. D‘Angelo, C. Crupi, A. Trimarchi, V. Conti Nibali, “Effects of medium-chain alcohols on the structure of phospholipid bilayers”, Il Nuovo Cimento, IN PRESS;

3. U. Wanderlingh, G. D‘Angelo, V. Conti Nibali, A. Trimarchi, C. Crupi ―Anisotropic dynamics in phosholipid membranes, a Fixed Energy Window neutron scattering study”, J. Chem. Phys. In press.

Rocco Vilardi

1. R. Vilardi, A. Ridolfo, S. Portolan, S. Savasta, O. Di Stefano, Quantum Complementarity of Cavity Photons

Coupled to a Three-Level System, to be published by Physical Review A;

2. Rocco Vilardi, articolo riguardante il trasferimento della coerenza, prossima pubblicazione su Le Scienze Web News, ISSN 1827-8922;

3. Rocco Vilardi, articolo riguardante il progetto ELENA, prossima pubblicazione su Le Scienze Web News, ISSN 1827-8922;

4. Rocco Vilardi, Alla ricerca del bosone di Higgs: nuova fisica al CERN?, Le Scienze Web News, 25 luglio 2011, ISSN 1827-8922;

5. Rocco Vilardi, Alessandro Ridolfo, Salvatore Savasta, Controllo ottico ultraveloce del dualismo onda corpuscolo, Le Scienze Web News, 28 marzo 2011, ISSN 1827-8922;

6. A. Ridolfo, R. Vilardi, O. Di Stefano, S. Portolan, and S. Savasta, All Optical Switch of Vacuum Rabi Oscillations: The Ultrafast Quantum Eraser, Physical Review Letters 106, 013601, January 05 2011;

7. Rocco Vilardi, Alessandro Ridolfo, Ultrafast Optical Control of vacuum Rabi Oscillations of a MicroCavity-Single Quantum Emitter System, ACTIVITY REPORT 2010, pp.69-72, Lorenzo Torrisi Editore, Dottorato di Ricerca in Fisica, Università degli Studi di Messina, c/o Dipartimento di Fisica, facoltà di Scienze-Università di Messina, ISSN 2038-5889.


140

PUBBLICAZIONI 2011 XXV Ciclo

Adriano Cacciola

1. Manipulation and Raman Spectroscopy with Optically Trapped Metal Nanoparticles Obtained by Pulsed Laser Ablation in Liquids, Messina E, Cavallaro E, Cacciola A, et al., JOURNAL OF PHYSICAL CHEMISTRY C Volume: 115 Issue: 12 Pages: 5115-5122 Published: MAR 31 2011;

2. Plasmon-Enhanced Optical Trapping of Gold Nanoaggregates with Selected Optical Properties, Messina E, Cavallaro E, Cacciola A, et al., ACS NANO Volume: 5 Issue: 2 Pages: 905-913 Published: FEB 2011;

3. Stratified dust grains in the interstellar medium. III Infrared cross-sections, Author(s): Iati M. A.; Cecchi-Pestellini C.; Cacciola A.; et al., 12th International Conference on Electromagnetic and Light Scattering by Nonspherical Particles - Theory, Measurements, and Applications, J. of Quantitative Spectroscopy & Radiative Transfer, Volume: 112 Issue: 11 Special Issue: SI Pages: 1898-1906, 2011.

Federico Di Bartolo

1. L.Torrisi; L. Giuffrida, D. Margarone, F. Caridi, F. Di Bartolo, Low energy proton beams from laser-generated

plasma, NIM in Physics A, 653, 140T (2011);

2. L. Torrisi, F. Caridi, F. Di Bartolo, A. Baglione, M. Cutroneo, Ion Production and Detection from Laser-Thin Targets Interaction, IEEE Transactions on Plasma Science, in press.;

3. F. Di Bartolo, F. Caridi, L. Torrisi, Mass Quadrupole Spectrometry applied to laser ion sources, Nucleonika., in press;

4. G. Castro, D. Mascali, F.P. Romano, L. Celona, S. Gammino, N. Gambino, D. Lanaia, R. Di Giugno, R. Miracoli, T. Serafino, F. Di Bartolo and G. Ciavola, Comparison between off-resonance and Electron Bernstein Waves heating regime in a Microwave Discharge Ion Source, Rev. Sc. Instr., (2011) in press.;

5. G. Castro, F. Di Bartolo, N. Gambino, D. Mascali, A. Anzalone, L. Celona, S. Gammino, R. Di Giugno, D. Lanaia, R. Miracoli, F.P. Romano, T. Serafino, S.Tudisco, Ion acceleration in non-equilibrium plasmas driven by fast drifting electron, Appl. Surf. Sc. (2011);

6. L. Torrisi, S. Cavallaro, S. Gammino, L. Andò, P. Cirrone, M. Cutroneo, R. Sayed, L. Giuffrida, F. Romano, F. Caridi, F. Di Bartolo, A.M. Visco, A. Baglione, C. Scolaro, Proton generation from LIS at INFN-LNS (LIANA project), INFN-LNS ACTIVITY REPORT 2010;

Maria Fisichella

1. Analysis of states in 13C populated in 9Be + 4He resonant scattering M. Freer, N. I. Ashwood, N. Curtis, A. Di Pietro, P. Figuera, M. Fisichella, L. Grassi, D. Jelavic Malenica, Tz. Kokalova, M. Koncul, T. Mijatovic M. Milin, L. Prepolec, V. Scuderi, N. Skukan, N. Soic, S. Szilner, V. Tokic D. Torresi, and C. Wheldon, Phys. Rev. C 84, 034317 (2011)

2. Fusion and direct reactions for the system 6He + 64Zn at and below the Coulomb barrier

V. Scuderi, A. Di Pietro, P. Figuera, M. Fisichella, F. Amorini, C. Angulo, G. Cardella, E. Casarejos, M. Lattuada, M. Milin, A. Musumarra, M. Papa, M. G. Pellegriti, R. Raabe, F. Rizzo, N. Skukan, D. Torresi, M. Zadr, Phys. Rev. C to be published

3. Li-α cluster states in 12B using 8Li + 4He inverse kinematics elastic scattering


141

D. Torresi, L. Cosentino, A. Di Pietro, C. Ducoin, P. Figuera, M. Fisichella, M. Lattuada, T. Lonnroth, C. Maiolino, A. Musumarra, M. Papa, M.G. Pellegriti, M. Rovituso, D. Santonocito, G. Scalia, V. Scuderi and E. Strano, M. Zadro, International Journal of Modern Physics E Vol. 20, No. 4 (2011) 1026–1029

4. Structure effects in the reactions 9,10,11Be+64Zn at the Coulomb barrier V. Scuderi, A. Di Pietro, L. Acosta, F. Amorini, M.J.G. Borge, P. Figuera, M. Fisichella, L.M. Fraile, J.Gomez-Camacho, H. Jeppesen, M. Lattuada, I. Martel, M. Milin, A. Musumarra, M. Papa, M.G. Pellegriti, F. Perez-Bernal, R. Raabe, G. Randisi, F. Rizzo, D. Santonocito, G. Scalia, O. Tengblad, D. Torresi, A.M. Vidal, M Zadro, Journal of Physics: Conference Series 267 (2011) 012012

5. Alpha structure of 12B studied by elastic scattering of 8Li EXCYT beam on 4He thick target M.G. Pellegriti, D. Torresi, L. Cosentino, A. Di Pietro, C. Ducoin, M. Lattuada, T. Lonnroth, P. Figuera, M. Fisichella, C. Maiolino, A. Musumarra, M. Papa, M. Rovituso, V. Scuderi, G. Scalia, D. Santonocito, M. Zadro, Journal of Physics: Conference Series 267 (2011) 012011

6. Halo effects on fusion cross section in 4,6He+64Zn collision around and below the coulomb barrier M Fisichella, V Scuderi, A Di Pietro, P Figuera, M Lattuada, C Marchetta, M Milin, A Musumarra, M G Pellegriti, N Skukan, E Strano, D Torresi, M Zadro, Journal of Physics: Conference Series 282 (2011) 012014

7. Structure effects and dynamics in fusion reactions of light weakly bound nuclei E. Strano, A. DiPietro, P. Figuera, M. Fisichella, M. Lattuada, C. Maiolino, A. Musumarra, M G Pellegriti, D Santonocito, V Scuderi, D Torresia, M Zadro, Journal of Physics: Conference Series 282 (2011) 012020

8. Fusion cross-section in the 4,6He + 64Zn collisions around the Coulomb barrier

M. Fisichella, Il Nuovo Cimento vol. 34C, 5 (2011)

Tino Minniti

1. T. Minniti and S. Santoro, ―Study of Nuclear equations of state:The ASY-EOS experiment at GSI‖ Activity Report 2010, Dottorato di Ricerca in Fisica, Università di Messina,. Torrisi Ed., 81-85, ISSN2038-

5889, 2011

Maria Romaniuk

1. M.V.Romaniuk, G.Giardina, G.Mandaglio, M.Manganaro, Meson Photoproduction and Baryon Resonances at BGOOD , Activity report 2010 , Università di Messina, ISSN 2038-5889 (2010) 95-98;

2. V.S.Olkhovsky, M.V.Romaniuk, Non-relativistic-particle and photon two-dimensional above-barrier penetration and sub-barrier tunneling through a barrier between initial and final free-motion regions along axis normal to both planar interfaces, Journal of Modern Physics, 2011, 2, 1166-1171, doi:10.4236/jmp.2011.210145. Published Online October 2011 G. Giardina, A. K. Nasirov, G. Mandaglio, F. Curciarello,V. De Leo, G. Fazio, M. Manganaro, M. Romaniuk, C. Saccà, Investigation on the quasifission process by theoretical analysis of experimental data of fissionlike reaction products, Journal of Physics: Conference Series 282 (2011) 012006, doi:10.1088/1742-6596/282/1/012006;

Simone Santoro

1. I.Lombardo, L.Acosta, C.Agodi, F.Amorini, A.Anzalone, L.Auditore, I.Berceanu, G.Cardella, S.Cavallaro,

.B.Chatterjee, E.De Filippo, G.Giuliani, E.Geraci, L.Grassi, J.Han, E.La Guidara, G.Lanzalone, D.Loria, C.Maiolino, T.Minniti, A.Pagano, M.Papa, S.Pirrone, G.Politi, F.Porto, F.Rizzo, P.Russotto, S.Santoro, A.Trifirò, M.Trimarchi, G.Verde, M.Vigilante

“N/Z effects on evaporation residue emission near fragmentation treshold” Proceeding of 14th International Conference on Information Fusion, FUSION 2011, JUL 5-8 2011, Chicago ILLINOIS USA - EPJ Web of Conferences 17 (2011) 16005


142

2. S. Santoro for CHIMERA and ASY-EOS Collaboration “Study of nuclear equations of state: the ASY-EOS experiment at GSI” Second International Symposium on Nuclear Symmetry Energy, NuSYM11, June 17-20 2011, at Smith College in Northampton, Massachusetts, USA.

3. S.Santoro for ASY-EOS Collaboration “Study of nuclear Equation Of State (EOS): the ASY-EOS experiment at GSI” The Nuclear Chemistry Gordon Research Conference, June 12-17 2011 Colby-Sawyer College, New London, New Hampshire, USA.

4. S.Santoro for ASY-EOS Collaboration “ASY-EOS experiment at GSI: Chimera results” ASYEOS collaboration meeting during the International Workshop on Multifragmentation and Related Topics – 2011 at GANIL from 2nd to 5th November 2011, Caen, France.

5. G.Cardella, L.Acosta, C.Agodi, F.Amorini, A.Anzalone, L.Auditore, I.Berceanu, M.BChatterjiee, E.DeFilippo, L.Grassi, E.La Guidara, G.Lanzalone, I.Lombardo, D.Loria, T.Minniti, A.Pagano, M.Papa, S.Pirrone, G.Politi, F.Porto, F.Rizzo, E.Rosato, P.Russotto, S.Santoro, A.Trifirò, M. Trimarchi, G.Verde, M.Vigilante

“Reactions with exotic beams using the CHIMERA detector at LNS” Conference on Structure and Dynamics of Nuclei far from Stability, September 15-16 2011, Dipartimento di Fisica e Astronomia dell‘Università di Catania.

6. G.Cardella, L.Acosta, C.Agodi, F.Amorini, A.Anzalone, L.Auditore, I.Berceanu, M.BChatterjiee, E.DeFilippo, L.Grassi, E.La Guidara, G.Lanzalone, I.Lombardo, D.Loria, T.Minniti, A.Pagano, M.Papa, S.Pirrone, G.Politi, F.Porto, F.Rizzo, E.Rosato, P.Russotto, S.Santoro, A.Trifirò, M. Trimarchi, G.Verde, M.Vigilante

“Use of fragmentation beams at LNS with CHIMERA detector” International Workshop on Multifragmentation and Related Topics – 2011 at GANIL from 2nd to 5th November 2011, Caen, France.

7. L. Acosta, T. Minniti, G. Cardella, G. Verde, F. Amorini, A. Anzalone, L. Auditore, M. Buscemi, A. Chbihi, E. De Filippo, L. Francalanza, E. Geraci, C. Guazzoni, E. La Guidara, G. Lanzalone, I. Lombardo, S. Lo Nigro, D. Loria, C. Maiolino, I. Martel, E.V. Pagano, A. Pagano, M. Papa, S. Pirrone, G. Politi, F. Porto, F. Rizzo, P. Russotto, A.M. SánchezBenítez, J.A. Dueñas, R. Berjillos, S. Santoro, A. Trifirò, M. Trimachi, M. Venhart, M. Veselsky, M. Vigilante

“FARCOS, a new array for femtoscopy and correlation spectroscopy” International Workshop on Multifragmentation and Related Topics – 2011 at GANIL from 2nd to 5th November 2011, Caen, France.

8. S. Santoro per la collaborazione ASY-EOS “Study of nuclear Equation Of State: the ASY-EOS experiment at GSI” Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.35

9. Acosta L., Agodi C., Amorini F., Anzalone A., Auditore L., Bardelli L., Berceanu I., Cardella G., Chatterjee M.B., De Filippo E., Grassi L., La Guidara E., Lanzalone G., Lombardo I., Loria D, Minniti T., Pagano A., Papa M., Pirrone S., Politi G., Porto F., Rizzo F., Russotto P., Santoro S., Trifirò A., Trimarchi M, Verde G., Vigilante M., “Misure con fasci di frammentazione ai LNS“

Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.174

10. Acosta L., Amorini F., Anzalone A., Auditore L., Cardella G., Chbihi A., De Filippo E., Francalanza L., Geraci E., Guazzoni C., La Guidara E., Lanzalone G., Lombardo I., Lo Nigro S., Loria D., Martel I., Minniti T., Pagano E.V., Pagano A., Papa M., Pirrone S., Politi G., Porto F.,Rizzo F.,Russotto P.,Santoro S., Trifirò A., Trimarchi M.,Verde G., Venhart M., Veselsky M., Vigilante M., “Il progetto FARCOS/EXOCHIM.”

Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.176

11. Acosta L., Amorini F., Anzalone A., Auditore L., Cardella G., Chbihi A., De Filippo E., Francalanza L., Geraci E., Guazzoni C., La Guidara E., Lanzalone G., Lombardo I., Lo Nigro S., Loria D., Martel I., Minniti T., Pagano E.V., Pagano A., Papa M., Pirrone S., Politi G.,Porto F., Rizzo F.,Russotto P.,Santoro S., Trifirò A., Trimarchi M., Verde G.,Venhart M., Veselsky M., Vigilante M.


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“Dinamica e spettroscopia da studi di correlazioni con FARCOS/CHIMERA.” Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.177

12. F. Amorini, R. Bassini, C. Boiano, G. Cardella, E. De Filippo, L. Grassi, C. Guazzoni, Member, IEEE, P. Guazzoni, M. Kiš, E. La Guidara, Y. Leifels, I. Lombardo, T. Minniti, A. Pagano, M. Papa, S. Pirrone, G. Politi, F. Porto, F. Riccio, F. Rizzo, P. Russotto, S. Santoro, W. Trautmann, A. Trifirò, G. Verde, P. Zambon, Student Member, IEEE, L. Zetta

“Light Charged Particle Identification by Means of Digital Pulse Shape Acquisition in the CHIMERA CsI(Tl) Detectors at GSI Energies”, submitted paper on IEEE Transactions, to be published.

PUBBLICAZIONI 2011 XXVI Ciclo

Francesca Curciarello

1. G. Giardina, A. K. Nasirov, G. Mandaglio, F. Curciarello, V. De Leo, G. Fazio, M. Manganaro, M. Romaniuk,

C. Saccà: ―Investigation on the quasifission process by theoretical analysis of experimental data of fissionlike reaction products‖, J. Phys.: Conf. Ser. 282, 012006 (1-20) (2011);

2. G. Fazio, G. Mandaglio, V. De Leo and F. Curciarello: “The Abrupt changes of the yellowed fibrils density on the Linen of Turin”, Rad. Eff. and Def. in Solids, iFirst (2011);

3. O. Povoroznik, O. K. Gorpinich, O. O. Jachmenjov, H. V. Mokhnach, O. Ponkratenko, G. Mandaglio, F. Curciarello, V. De Leo, G. Fazio and G. Giardina: ―High-lying 6Li levels at exicitation energy of around 21 Mev”, J. Phys. Soc. Jpn. 80 (2011) 094204.

Mariapompea Cutroneo

1. L. Torrisi, S. Cavallaro, M. Cutroneo, D. Margarone, S. Gammino

―Proton emission from a laser ion source‖ Participation to 14 th ICIS 2011 Int. Conference, 12-16 Sept., Giardini Naxos (ME), Italy, Accepted from Review of Scientific Instruments, 2011, in press.

2. D. Margarone, J. Krasa, J. Prokupek, A. Velyhan, L. Torrisi, A. Picciotto, L.Giuffrida, S. Gammino, P. Cirrone, M. Cutroneo, F. Romano, E. Serra, A. Mangione, M. Rosinski, P. Parys, L. Ryc, J. Limpouch, L. Laska, K. Jungwirth, J. Ullschmied, T. Mocek, G. Korn and B. Rus ―New methods for high current fast ion beam production by laser-driven acceleration‖

Participation to 14 th ICIS 2011 Int. Conference, 12-16 Sept., Giardini Naxos (ME), Italy, Accepted from Rev. Sci. Instr., 2011, in press.

3. L. Torrisi, S. Cavallaro, M. Cutroneo, L. Giuffrida, J. Krasa, D. Margarone, A. Velyhan,

J. Kravarik, J. Ullschmied, J. Wolowski, A. Szydlowski, M. Rosinski ―Monoenergetic proton emission from nuclear reaction induced by high intensity laser- generated plasma‖, Participation to 14 th ICIS 2011 Int. Conference, 12-16 Sept., Giardini Naxos (ME), Italy, Accepted from Review of Scientific Instruments, 2011, in press. 4. L. Torrisi, A. Italiano, E. Amato, F. Caridi, M. Cutroneo, C.A. Squeri, G. Squeri and A.M.

Roszkowska ―Radiation effects on poly(methyl methacrylate) induced by pulsed laser irradiations. Radiation Effects & Defects in Solids 2011, in press.


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5. M. Cutroneo, Relazione su invito alla Conferenza: ―X Giornata di Studio BIOINGEGNERIA - Facoltà di Ingegneria Università di Catania - 1 luglio 2011‖ col lavoro: ―Fisica dei laser e loro interazione con la materia‖, Proceeding 2011 in press.

6. Proceedings Conferenza 5th PPLA (Plasma Production by Laser Ablation), Catania, 21-23 Set. 2011, col lavoro ―Laser ablation coupled to mass quadrupole spectrometer (LAMQS) and X-rays fluorescence for applications in cultural heritage‖, in press.

7. Proceedings Conferenza 5th PPLA (Plasma Production by Laser Ablation), Catania, 21-23 Set. 2011, col lavoro ―Proton emission from resonant laser absorption and self-focusing effects from hydrogenated structures”, in press.

8. Proceedings Conferenza 5th PPLA (Plasma Production by Laser Ablation), Catania, 21-23 Set. 2011, col lavoro ―XPS and XRF depth patina profiles of ancient silver coins‖, in press.

Veronica De Leo

1. G. Giardina, A.K. Nasirov, G. Mandaglio, F. Curciarello, V. De Leo, G. Fazio, M. Manganaro, M. Romaniuk, C. Saccà, Investigation on the quasifission process by theoretical analysis of experimental data of fissionlike reaction products, Journal of Physics: Conference Series 282 (2011) 012006;

2. O. Povoroznyck, O.K. Gorpinich, O. O. Jachmenjov, H.V. Mokhnach, O.Ponkratenko, G.Mandaglio, F.Curciarello, V. De Leo, G. Fazio, and G. Giardina, ―High-Lying 6Li Levels at Exicitation energy of around 21 Mev‖, J. Phys. Soc. Jpn. 80 (2011) 094204;

3. G. Fazio, G. Mandaglio, V. De Leo and F. Curciarello: ―The Abrupt changes in the yellowed fibril density in the Linen of Turin‖, Rad. Eff. and Def. in Solids, iFirst (2011).

Rania Sayed

1. M. G. Donato, P. G. Gucciardi, S. Vasi, M. Monaca, R. Sayed, G. Calogero, P.H. Jones, O.M. Maragò,

"Raman optical trapping of carbon nanotubes and graphene", Proceedings of CARBOMAT 2011, Catania, 5th-7th December 2011;

2. Proceedings accepted for a poster presentation at CARBOMAT 2011, Workshop on Carbon-based low-dimentional Materials, Catania, 5th-7th December, 2011.

Roberto Stassi

1. O. Di Stefano, R. Stassi, A. Ridolfo, S. Patané, and S. Savasta, Phys.Rev. B 84, 085324 (2011)


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Foto 2a Giornata di Studio

del Dottorato di Ricerca in Fisica dell‘Università di Messina

8 Novembre 2011, Facoltà di Scienze M.M.F.F.N.N.

Biblioteca Centralizzata V.le F. S. D‘Alcontres 31

S. Agata, Messina


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INDICE AUTORI Artoni P pag. 89 Aversa M C 13 Cacciola D 21 Calogero G 61, 89 Caridi F 25, 55 Castro G 25 Celona L 25 Colonna M 101 Curciarello F 37, 65, 77 Cutroneo M 71 D‘Andrea C 61, 89 De Leo V 37, 65, 77 Di Bartolo F 25 Di Giugno R 25 Di Pietro A 31 Di Stefano O 85, 93 Di Toro M 101 Donato M G 81 Donato P 49 Fazio B 61, 89 Figuera P 31 Fina N 93 Fisichella M 31 Gammino S 25 Giaquinta P V 47 Giardina G 37, 65, 77 Greco V 101 Gucciardi P G 61, 81, 89 Irrera A 89 Lanaia D 25 Lattuada M 31 Magaudda D 15 Mandaglio G 37, 65, 77 Maragò O M 61, 81, 89, 93 Marchetta C 31 Mascali D 25 Micali N 61 Minniti T 33 Miracoli R 25 Musumarra A 31 Pellegriti M G 31

Ridolfo A 93 Rifici S 97 Romaniuk M 37, 65, 77 Ruiz C 31 Santoro S 41 Savasta S 85, 93, 109 Sayed R 81 Scardina F 101 Scuderi V 31 Shotter A 31 Stassi R 85 Strano E 31 Torresi D 31 Torrisi L 9, 25, 55, 71 Trimarchi A 105 Vilardi R 109 Villari V 61 Volpe G 81 Zadro M 31


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Print: Runner Digital Printing – Catania – Italy 31 Dicembre 2011 All right Reserved


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Dottorato di Ricerca in Fisica Facoltà di Scienze

Dipartimento di Fisica Università di Messina

V.le F. Stagno D’Alcontres S. Agata, Messina, Italy Phone: +39 090 6765052

Fax: +39 090 395004 e-mail: Lorenzo. [email protected]

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