Optical Limiting

CHIN.PHYS. LETT. Vol. 28, No. 11 (2011) 116101

Optical Limiting Properties of Ag-Cu Metal Alloy Nanoparticles Analysis byusing MATLAB *

WANG Yu-Hua()1**, LI Hui-Qing()2, LU Jian-Duo()1, WANG Ru-Wu()11Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, and Department of

Applied Physics, Wuhan University of Science and Technology, Wuhan 4300812Department of Endocrinology, Union Hospital, Tongji Medical College, Huazhong University of Science and

Technology, Wuhan 430022

(Received 6 June 2011)Ag-Cu alloy nanoparticles were formed by sequential ion implantation (Ag and Cu) in silica using a metal vaporvacuum arc (MEVVA) ion source. Third-order nonlinear optical properties of the nanoparticles were measuredat 1064 nm excitations using the Z-scan technique. Curve fitting analysis, based on the MATLAB features forAg-Cu alloy nanoparticle optical limiting experiments, is used. The results show that Ag-Cu alloy nanoparticlesdisplay a refractive optical limiting effect at 1064 nm.

PACS: 61.46.+W, 61.72.Ww, 42.65.K DOI:10.1088/0256-307X/28/11/116101

Recently, increasing attention has been focusedon the third-order nonlinear susceptibility and thephotorefractive effect of noble-metal clusters embed-ded in dielectric matrices.[13] Third-order nonlinear-ities of metal/dielectric composite materials are in-fluenced not only by the type and size of the embed-ded metal clusters, but also by the dielectric constant,thermal conductivity and heat capacity of the dielec-tric matrices.[46] Amongst the nanoparticles studiedearlier, high nonlinear absorption and nonlinear re-fraction coefficients were found in copper and coppercontaining nanomaterials.[7,8] For silver, the nonlinearrefractive index changes from positive to negativeupon the growth of clusters.[9] Potential applicationsof optical limiters in the protection of sensors from in-tense laser pulses have motivated great efforts to de-sign new nonlinear optical systems.[10]

Ion implantation has been utilized to producehigh-density metal colloids in glass. The high precipi-tate volume fraction and the small size of nanopar-ticles in glass lead to a third-order susceptibilitygreater than those for the corresponding metal-dopedsolid. The third-order nonlinear optical responses ofthe metal-nanoparticle-glass composites can be un-derstood from the framework of dielectric and quan-tum confinement effects. The optical nonlinearitiesand limiting effects of the nanocomposites with metalnanoparticles can be significantly enhanced by in-creasing the number density and the size of metalparticles.[11] The application aspects of materials areclosely related to the change of optical properties ver-sus the nanoparticle structure.

Currently, optical limiting results are obtainedthrough the analysis of experiments, including the

completion of specific research tasks. Engineers andtechnicians drawings are usually analyzed using aux-iliary tools, such as MicroCal Origin, Microsoft Excel,and so on. Although these analysis tools supplementvarious experimental results, all of them are in theform of direct application software, which is not com-prehensive enough to fit curves, and some limitationstherefore still remain in the analysis of experimentaldata.

MATLAB incorporates science, engineering calcu-lations and visual figure functions, and has a Win-dows interface design method. It has a stronger op-erating ability, powerful and intelligent mapping, andhigher programming efficiency; in particular, it canbe used for application development in this field. Inour previous work, the optical limiting properties ofAg/Cu and Cu/Ag mixture nanoparticles have beenstudied.[12,13] In this Letter, Ag-Cu alloy nanoparti-cles were prepared by Ag/Cu sequential ion implan-tation into silica using a MEVVA source implanteraccording to the experimental protocol. We focus ourinterest on studying the nonlinear optical propertiesand optical limiting properties of this kind of metalalloy nanoparticle.

Silica slides were sequentially implanted with 5 1016 Ag+ ions/cm2 and 5 1016 Cu+ ions/cm2 us-ing a MEVVA source implanter at room temperature.The acceleration voltages of 43 kV for Ag and 30 kVfor Cu, respectively, were chosen to reach the sameprojected range for the implanted species. The fluxdensity was 2mA/cm2. Optical absorption spectrawere recorded at room temperature using a UV-VISdual-beam spectrophotometer with wavelengths from900 nm to 200 nm. The measurements of the third-

*Supported by the National Natural Science Foundation of China under grant(Nos 10805035 and No.11191240126).**Corresponding author. Email: [email protected] equally to this work.c 2011 Chinese Physical Society and IOP Publishing Ltd

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Chin. Phys. Lett.References










order optical nonlinearities of the sample were carriedout using the standard Z-scan method. The excita-tion source is a mode-locked Nd:YAG laser (PY61-10,Continuum) with a pulse duration of 38 ps and a rep-etition frequency of 10Hz. The 1064 nm wavelengthis used for excitation in the experiment. The detectoris a dualchannel energy meter (EPM2000). It has aconverging lens of = 260mm and the radius of theGaussian beam spot at focal waist 0 is 44.7m. Inthe Z-scan test, the sample was moved step by stepalong the propagation direction of the Gaussian beamunder the control of a computer. Meanwhile, a detec-tor was used to monitor the transmitted laser powerand the signals were sent back to the computer tobe recorded. Nonlinear refraction and nonlinear ab-sorption were performed by both open- and closed-aperture Z-scans of a series of the samples at roomtemperature.

300 400 500 600 700 800

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Cu

Ag-Cu

Ag

Optical density

Wavelength (nm)

Fig. 1. Optical density vs wavelength for the Ag/Cu se-quentially implanted sample with Ag 5 1016 and Cu5 1016 ions/cm2, Ag implanted sample with a dose of1 1017 ions/cm2 and Cu implanted silica with a dose of1 1017 ions/cm2.

0.6

0.8

1.0

1.2

1.4

-30 -20 -10 0 10 20 30

0.6

0.8

1.0

1.2

1.4

(a)

Normalized transmittance

Experiment

Theoritical fit

(b)

(mm)

Fig. 2. Normalized transmitance with closed-aperture(a) and open-aperture (b) Z-scan experiment results at1064 nm. Solid line: theoretical curve.

Figure 1 shows the optical absorption spectra ofAg/Cu sequentially implanted samples. For compar-ison, the optical absorption spectra of the Ag im-planted sample with a dose of 1 1017 ions/cm2 atan energy of 90 keV and Cu implanted sample witha dose of 1 1017 ions/cm2 at energy of 60 keV arealso shown in the figure. The surface plasmon reso-nance (SPR) peak position is 442 nm for the sampleAgCu1:1, which lies between those of pure Ag and Cunanoparticles (about 400 and 570 nm, respectively).Our previous work[14] has shown that intermetallicAg-Cu alloy nanoparticles can be formed instead oftwo separated Ag and Cu nanoparticles.

The difference between the formed Ag-Cu alloynanoparticles and the Ag-Cu mixture nanoparticleslies in different methods of ion implantation. Inthis study, the implantation of Ag and Cu was car-ried out by using a MEVVA source ion implanter.The MEVVA ion source is a high-current metal-ionsource. The ion flux densities for both elements are2mA/cm2, which is much larger than those in the pre-vious work.[12] In that work, the flux densities of Agand Cu ions were 1A/cm2 and 1.5A/cm2, respec-tively. The alloy formation is related to the enhanceddiffusion of Cu in small Ag clusters, just like addingCu to Ag by the heat generated from the implantationthat gives rise to high local temperatures.[15]

The third-order nonlinear absorption and refrac-tion are investigated by Z-scan techniques.[16] Thistechnique is simple and sensitive for studying nonlin-ear optical properties and determining the sign of thenonlinear refractive and absorption indices. The open-and closed-aperture Z-scan curves are theoretically fit-ted by[16]

() =

=0

[0()](1 + 2)( + 1)3/2

, ( 0)(1)

() = 1 +40

(2 + 9)(2 + 1), (2)

where = /0, is the normalized transmittanceand is the distance along the lens axis in the farfield. The nonlinear refractive index is calculated by0 = (2/)0eff . Here, 2/ is the wave vectorof the incident laser, 0 is the intensity of the laserbeam at the focus ( = 0), eff is the effective thick-ness of the sample, which can be calculated from thereal thickness and the linear absorption coefficient0, in the form of eff = [1 exp(0)]/0.

The third-order nonlinear optical property of thesample was measured at 1064 nm. If the samplespossess nonlinear absorptive properties, the closed-aperture transmittance should be affected by the non-linear refraction and absorption. The determinationof is less straightforward from the closed-aperturescans. It is necessary to separate the effect of nonlin-

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ear absorption by closed/open-aperture. The experi-mental results of the Z-scan for Ag-Cu alloy nanopar-ticles are shown in Fig. 2. The open-aperture Z-scan(b) shows no nonlinear signal, which indicates thatthe sample has no nonlinear absorption at 1064 nm.The peak-valley configuration in Fig. 2(a) indicatesthe negative sign of the nonlinear refractive index(


It is more likely to happen in high order polynomialcases. For this reason, we rarely used more than a 6-order polynomial, unless the polynomial we used wasreal polynomial. Generally, we choose = 3 or = 5.Here, because the amount of data is not very large,the regularity is good. Considering the computer run-ning time, the curve fitting accuracy, smoothness andso on, we choose = 8. We can see that the fittingsample image output values increase with the increaseof . However, the rate of increase of the output valueis gradually reduced to zero and there is a drop in thecurve tail section. The fitting curve aligns well withthe optical limiting characteristics of the curve, indi-cating that Ag-Cu alloy nanoparticles play a part inthe optical limiting effect.

In summary, Ag-Cu alloy nanoparticles exhibit in-teresting nonlinear optical properties and optical lim-iting properties. The analysis methods from MAT-LAB we choose in this study are different from theprevious work.[12] Here we apply the index regressioncurve-fitting method to obtain the fitting procedure,which reflects the trend of optical limiting propertiesof the sample. Then, we apply the least square curve-fitting method to determine the values for the shapefactor. Comparing the different orders of the polyno-mial, we find that = 8 can fit well with the experi-mental results. As far as the samples optical limitingcharacter and its physical origin, we think that theoptical limiting character of the sample comes fromthe optical Kerr effect. Because there is no nonlin-ear absorption at 1064 nm, the nonlinear refractionplays the whole role on the optical limiting characterof these kinds of samples.

In this study, metal alloy nanoparticles in silicahave been synthesized by sequential ion implantationof Ag and Cu ions using MEVVA. We report the ex-perimental observations of the nonlinear optical re-sponses of Ag-Cu alloy nanoparticles using picosecondlaser pulses. For 1064 nm excitation, the sample hasno nonlinear absorption and the nonlinear susceptibil-

ity (3) is 3.5107 esu, which arises from the nonlin-ear refraction contribution. Moreover, the optical lim-iting effect at 1064 nm is also observed. We apply theindex regression analysis and the least square curve-fitting method analysis by using MATLAB software.Basically, the curve-fitting reflects that the sample hasan optical limiting property at the near-infra-red field.MATLAB is effective for the study of optical limits ofmaterials and further studies are in progress.

References[1] Stepanov A L 2011 Rev. Adv. Mater. Sci. 27 115[2] Battaglin G, Calvelli P, Cattaruzza E, Gonella F, Polloni

R, Mattei G and Mazzoldi P 2001 Appl. Phys. Lett. 783953

[3] Falconieri M, Salvetti G, Cattaruzza E, Gonella F, MatteiG, Mazzoldi P, Piovesan M, Battaglin G and Polloni R 1998Appl. Phys. Lett. 73 288

[4] Wang Y H, Ren F, Wang Q Q, Chen D J, Fu D J and JiangC Z 2006 Phys. Lett. A 357 364

[5] Haglund R F, Jr, Yang L, Magruder R H, Wittig J E, BeckerK and Zuhr R A 1993 Opt. Lett. 18 373

[6] Wang Y H, Wang Y M, Lu J D, Ji L L, Zhang R G andWang R W 2010 Opt. Commun. 283 486

[7] Wang Y H, Wang Y M, Lu J D, Ji L L, Zhang R G andWang R W 2009 Physica B 404 4295

[8] Wang Y H, Jiang C Z, Ren F, Wang Q Q, Chen D J andFu D J 2006 Phys. E 33 244

[9] Ganeev R A, Ryasnyansky A I, Kamalov S R, Kodirov MK and Usmanov T 2001 J. Phys. D: Appl. Phys. 34 1602

[10] Ryasnyanskiy A I, Palpant B, Debrus S, Pal U and StepanovA L 2007 Opt. Commun. 273 538

[11] Francois L, Mostafavi M and Belloni J 2000 J. Phys. Chem.B 104 6133

[12] Wang Y H, Wang Y M, Han C J, Lu J D, Ji L L and WangR W 2010 Vacuum 85 207

[13] Wang Y H, Wang Y M, Han C J, Lu J D, Ji L L and WangR W 2010 Physica B 405 2848

[14] Wang Y H, Jiang C Z, Ren F, Wang Q Q, Chen D J andFu D J 2007 J. Mater. Sci. 42 7294

[15] Gonella F, Mattei G, Mazzoldi P and Sada C 1999 Appl.Phys. Lett. 75 55

[16] Sheik-Bahae M, Said A A, Wei T H, Hagan D J and VanStryland E W 1990 IEEE J. Quantum Electron. 26 760

[17] Sheik-Bahae M, Hagan D J and Van Stryland E W 1990Phys. Rev. Lett. 65 96

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TitleFig. 1Fig. 2Eq. (1)Eq. (2)Eq. (3)Eq. (4)Fig. 3Fig. 4References

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Optical Limiting