Fullerene-oxygen-iodine laser (FOIL) Physical principles

Fullerene–oxygen–iodine laser „FOIL…. Physical principles *O. B. Danilov, I. M. Belousova, A. A. Mak, V. P. Belousov, A. S. Grenishin, V. M. Kiselev,A. V. Kris’ko, T. D. Murav’eva, and E. N. Sosnov

Scientific Research Institute of Laser Physics, St. Petersburg

A. N. Ponomarev

AO Astrin-Holding, St. Petersburg~Submitted August 12, 2003!Opticheski� Zhurnal70, 79–86~December 2003!

This paper discusses the physical principles involved in creating a fullerene–oxygen–iodine laser~FOIL! with optical ~including solar! pumping. The kinetic layout is discussed, and it isshown that the limiting efficiency of a FOIL can exceed 40% relative to the energy absorbed bythe fullerenes. Experimental results of the lasing of singlet oxygen in liquid media~solutionsand suspensions! and in solid-state structures containing both fullerenes and fullerenelikenanoparticles~FLNs! are presented. It is experimentally shown to be possible to releaseoxygen in the vapor phase by organizing the boiling of a solution~suspension!, as well as by agasdynamic desorption wave from solid-state FLN- or fullerene-containing structures.Preliminary experimental results are presented of the pulsed lasing of a FOIL with opticalpumping, using the initial photodissociation of iodide to provide atomic iodine in the lasing zone.The principle of spectral separation of optical pumping is implemented in experiments onthe lasing of a FOIL. ©2003 Optical Society of America

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INTRODUCTION

Iodine lasers, which occupy an important place in moern laser physics, are developing along two main directiophotodissociation iodine lasers, using UV optical pumpiand chemical oxygen–iodine lasers~COILs!, using singletoxygen1DO2 obtained from a chemical reaction for puming. By using these two approaches, it has been possibmaximize the pulse energy and the laser radiation powethe near-IR region.

The Institute of Laser Physics has played an appreciarole in developing photodissociative iodine lasers. It is hthat a photokinetic model of the laser was developed, thestudies of optical inhomogeneities and magnetooptic pnomena in active media were carried out, high-efficienpowerful pump lamps were developed, record values ofspecific energy parameters and record efficiencies~2%! of aphotodissociation iodine laser with lamp pumping1 wereachieved for a single-lamp laser module with a radiationergy of about 1 kJ, and the physical principles of a photodsociation iodine laser with solar pumping were develope2

Here we consider the next important step in the devopment of iodine lasers: the fullerene–oxygen–iodine la~FOIL!,3 we present experimental results on the lasingsinglet oxygen when photons interact with fullerenes in luid media and in solid-state structures,4 and we also presenthe first results on the lasing of a FOIL. However, first letdefine the main principles that induced us to take onproblem. There are two of these principles:

1. The possibility of developing a competitive technlogical multi-kilowatt FOIL with optical pumping~i.e., with-out a chlorine chemical cycle of singlet-oxygen lasing, asa COIL!. Here it should be pointed out that an oxygeniodine laser is attractive to the developers of laser mate

898 J. Opt. Technol. 70 (12), December 2003 1070-9762/2003/1

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processing complexes, because the radiation wavelengl51.315mm matches the spectral characteristics of fiboptic cable. Thus, for example, Ref. 5 describes the transof 11-kW laser radiation from an iodine laser over a fiber

2. The possibility of developing a high-efficiency FOIwith solar pumping.

THE KINETIC LAYOUT AND AN ESTIMATE OF THELIMITING EFFICIENCY OF A FOIL

The kinetic layout of a FOIL is shown in Fig. 1. Thishows a simplified system of the energy levels of fullereC60, molecular oxygen O2, and atomic iodine that are mosimportant for the problem under consideration and the mtransitions when they interact. It should be understood tthe picture of the levels in Fig. 1a is extremely conventionsince each electronic level has a fairly complex vibrationarotational structure~besides, of course, atomic iodine, whichas its own hyperfine level structure!. According to Fig. 1, anoptical pump photon is absorbed by fullerene in the singstate channel. Then an intrasystem nonradiative transitioncurs in fullerene in 1 ns from singlet stateS1 to triplet stateT1 , whose lifetime under various conditions is estimated431025– 1022 sec. TheT1 state of fullerene is the first energy accumulator in the kinetic layout of a FOIL. One of thbest quenchants of theT1 state is molecular oxygen. In thpresence of oxygen, theT1 lifetime decreases to 330 ns. Thphenomenon was studied in Ref. 6 in a solution of C60 andO2 in C6H6 while the solution was irradiated by laser pulswith l50.532mm. Singlet oxygen1DO2 then appearedwith a quantum yield of 0.96, which was recorded from lminescence withl51.268mm. Reference 6 also determinethe constants of two very important reactions: that for extation transport from fullerene in theT1(3C60) state to oxy-

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FIG. 1. Kinetic layout of a FOIL:~a! diagram of the most important energy levels of fullerene, oxygen, and iodine;~b! energy-conversion diagram of a pumphoton to the energy of a lasing photon;~c! absorption spectrum of the fullerenes C60 , C70 , C76 , C78 , and C84 , and the emission spectrum of a source of ttype of an absolute blackbody~ABB! with a radiance temperature of 6500 K.

gen, with the formation of 1DO2: K2'3.3310212 cm3 sec21; and the quenching constant of1DO2 by

899 J. Opt. Technol. 70 (12), December 2003

the fullerene C60: K3'8.0310216 cm3 sec21. Our firstestimates,3 using the constantsK2 andK3 ~and they differ by

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a factor of 4000!, showed that it was possible to obtain siglet oxygen (1DO2) when fullerenes were optically pumpewith a concentration ratio of singlet and ordinary oxygen tsubstantially exceeded the necessary value of this ratioreliable lasing of an oxygen–iodine laser.

Here let us consider in more detail the lasing mechanof singlet oxygen1DO2 when triplet3C60 interacts with O2.It can be seen from Fig. 1a that it is virtually impossibledirectly transfer excitation from3C60(T1) to 1DO2 becauseof the large energy difference of the corresponding levelsthe same time, there is virtually exact resonance of3C60(T1)with the next higher singlet state of oxygen,1Sg

1O2. Theexcitation-transfer process from the triplet stateT1 offullerene to the1DO2 state therefore occurs in two stageFirst 3C60(T1)→1Sg

1O2 and then excitation is transferrefrom 1Sg

1O2 to 1DO2. This is only possible when there iinteraction with a certain supplementary~third! molecule,which, as a rule, is either a solvent6 or a buffer gas.7 In Ref.6, when C6H6 was used a buffer gas in a wide rangepressures, the lifetime of1Sg

1O2 was in the range10210– 1029 sec with virtually complete transition to th1DgO2 state. In Ref. 6, when C6H6 was used a solvent fofullerene and oxygen, luminescence from1Sg

1O2 (l50.762mm) in general was not observed, while the quatum yield of 1DgO2 was ~as indicated above! 0.96 for irra-diation by a laser pulse (l50.532mm) with a width ofabout 10 ns.

The further course of events in accordance with the csical COIL diagram~see Figs. 1a and 1b! is as follows: Sin-glet oxygen1DgO2 donates its energy to atomic iodine in th2P1/2I state, which is the upper working state of an iodilaser. Here an essential parameter that also determinelaser’s efficiency is the consumption of singlet oxyg1DgO2 to produce one lasing photon (l51.315mm). Thisvalue essentially depends on the method of producing atoiodine in the singlet-oxygen medium. The fact that a FOuses broad-band optical pumping provides a unique possity of using here the UV part of this pumping for the photdissociation of the iodide RI~where R is a radical of typeCnFm or CnHm), with the formation of atomic iodine immediately in the upper2P1/2 state. We should point out that ithis case we do not introduce any additional losses intospectral part of the optical pumping that is most favorableabsorption by fullerenes and for obtaining their triplet staTherefore, it is easy to understand that we can assumethe consumption of singlet oxygen for one lasing phoequals approximately unity. This means that the maximphysical efficiency of a FOIL can be estimated as the ratiothe energy of a lasing photon to the energy of a pump pton, i.e., a quantity that exceeds 40% relative to the eneabsorbed by the fullerenes. It is shown in Fig. 1c that,using a mixture of fullerenes with various numbers of carbatoms, it is possible to absorb up to 82% of the solar eneThis means that a FOIL with solar pumping can haveefficiency greater than 33%. It should be pointed out thatnot only fullerenes that can be efficient producers of singoxygen. Fullerene-like nanoparticles~FLNs! are also inter-esting in this respect, since they have transverse dimens


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of tens of nanometers, and this makes it much easiernumber of cases to construct specific devices based on thOne of the most successful FLNs is so-called astralewhich is a polyhedral multilayer helixlike carbon nanostruture ~Fig. 2!. The transverse size of astralene is 25–100 n

In setting up the experimental work at the beginnistage, we concentrated on three approaches:

1. Measurement of the quantum yield of singlet oxygwhen fullerenes and FLNs are used in solutions and sussions. We concentrated on suspensions, because it is by ususpensions that it will apparently be simpler to solve prlems of the necessary concentrations of fullerenes andcomposition of the working mixture.

2. Proof of the theorem of the existence of the efficieyield of singlet oxygen in the vapor phase.

3. Implementation of a FOIL with an initial photodissociation cycle and spectral separation of broad-band optpumping.

MEASURING THE GENERATION OF SINGLET OXYGEN

The appearance of singlet oxygen was experimentmeasured from luminescence signals withl150.762mm(1Sg

1O2) and l251.268mm (1DgO2) when the opticalpump photons, the fullerenes,~or FLNs! and oxygen interact.

Two types of optical pumping were used:

• Laser pumping: pulses about 10 ns wide,l50.532mm,pulse energy up to 0.6 J/cm2.

• Lamp pumping~with a xenon lamp! with a pulse about250 ms wide, where the pulse energy is chosen as a fution of the experimental conditions and can appreciaexceed the energy of a laser pulse.

The individual experiments used filters for spectral crection of the lamp pumping, so that its spectral distributiwould approximate a solar-like spectrum.

The objects of the investigation were solutions of C60

and O2 in CCl4 , as well as suspensions of FLNs~astralenes!in CCl4 , where oxygen was simultaneously dissolved. B

FIG. 2. Electron micrograph of astralenes~a polyhedral, helixlike carbonnanostructure! ~FLNs!.

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sides this, solid-state fullerene-containing membranes wstudied. The latter included three types of structures:
• coatings made from fullerenes on optical surfaces;• coatings made from fullerenes inside the pores of mic

channel plates;• structures in the form of two microcell metal grids, b

tween which powdered astralene was placed.

The solid-state objects~membranes! were either placedin a chamber with gaseous oxygen, or oxygen was pasthrough them.

The quantum yield of singlet oxygen was measuredliquids ~solutions and suspensions! using laser pumping thamade it possible to make precise measurements of the alute values.

Measurements of the quantum yield~QY! of singlet oxy-gen in a solution of C60 and O2 in CCl4 with laser pumpinggave a value of QY'0.96.

The quantum yield of singlet oxygen in a suspensionastralene and a solution of O2 in CCl4 with laser pumpingwas QY'0.64. This value can be regarded as very high iis understood that astralene has a transverse size of 25nm and gives a wider possibility of constructing a singoxygen generator with optical pumping.

Figure 3 shows typical luminescence pulses withl1

50.762mm and l251.268mm, obtained in a solution oC60 and O2 in CCl4 with laser pumping. The width of thespulses lies in the millisecond range.

When one goes to lamp pumping and successivelycreases the pulse energy of the lamp pumping, the lumicence pulse width increased to 10 ms or more~see Fig. 4!.

Figure 5 shows the luminescence pulses of singlet ogen ~Figs. 3 and 4! in a semi-log plot. The slopes of thcurves shown here in practice determine the lifetime of sglet oxygen under specific conditions.

Analysis showed that the first sharp change of the tidependence of ln(Plum) correlates with boiling up of the solution and the formation of a gas bubble, i.e., with thereleaseof singlet oxygen into the vapor phase. The lifetime of sin-glet oxygen increases in this case. The second sharp chof this dependence~a decrease of the lifetime of singlet oxygen! is associated with the transition of the vapor state ofmedium into the liquid state. In practice, the fact that tslope of the latter section of the luminescence curve of1DO2

FIG. 3. Luminescence pulses of singlet oxygen accompanying laser puing of a fullerene-containing solution.


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exactly corresponds for lamp pumping and for laser pump~where there is no boiling of the solution! is an additionalproof of the correctness of the interpretation of the expemental results.

The result obtained on the release of singlet oxyg1DO2 into the vapor phase is fundamental.

Figure 6 shows the luminescence pulses of singlet ogen obtained as a result of the interaction of optical lapumping, solid-state fullerene-containing devices, and ogen. The following were used: a C60 coating on an opticalglass surface, a C60 coating inside the channels of a microchannel plate~Fig. 6a!, and a device based on powdereastralene~FLNs! ~Fig. 6b!.

It can be seen that the luminescence pulses consistwo characteristic parts: an initial peak, about 1026 sec wide,and a tail, whose width is 10–100ms.

By analyzing the experimental conditions, we arrivedthe conclusion that the luminescence peak is determinedsinglet oxygen that is sorbed by the solid-state fullere

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FIG. 4. Luminescence pulse of singlet oxygen accompanying lamp pumof a fullerene-containing solution.

FIG. 5. Luminescence pulses in a semi-log plot.

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FIG. 6. Luminescence pulses of singlet oxygen using solid-state fullercontaining devices:~a! fullerene coatings,~b! powdered astralene.


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the luminescence pulse is associated with gasdynamic wdesorption of singlet oxygen from the solid-state fullerestructure formed under the action of pulsed optical pumpiWe decided to use this desorption wave of singlet oxygenpumping the FOIL with the use of preliminary photodissciation of alkyliodide.

LASER GENERATION OF ATOMIC IODIDE IN THEFULLERENE–OXYGEN–IODINE SYSTEM

To obtain a lasing effect, a laser was used~see Fig. 7!consisting of a quartz cell with internal diameter 10 mm alength of the active part determined by the interelectrodeof the pump lamp of 500 mm. The cell windows are placat Brewster’s angle. The coating of the inner surface ofcell wall with fullerene C60 was deposited chemically. Thtransmittance of the coating was 20% in the UV and 60%the visible region. Pumping was done with a pulsed xenband lamp~accumulated electric energy 0.5 kJ! surroundingthe laser cell, and therefore the magnetic field in the acmedium of the laser equals zero during the entire pulse.laser cavity was formed by flat mirrors with reflectances99.9% and 99%. This ensured a low lasing threshold andabsence of magnetooptic phenomena that could affectamplitude–time lasing characteristics of the iodine laser.

The laser cell was initially filled with C3F7I at a pressureof 10–15 Torr. The ordinary photodissociation regime ofiodine laser was implemented, with the lasing pulse showFig. 8a. Here the lasing pulse width virtually coincides wthe pump pulse width and equals about 10ms. After beingpumped out, the laser cell was filled with oxygen, which wheld in the cell for several hours, during which it was sorbby the fullerene coating. The residues of oxygen wepumped out, and the cell was again filled with C3F7I. Thepumping was reduced to the threshold value, and the setivity of the detector that records the lasing pulse was mamized. The result is shown in Fig. 8b. This shows a coparatively long luminescence pulse of atomic iodinel51.315mm) on the background of which two peaks adistinguished: the first peak is the lasing determined byphotodissociation of C3F7I, and the second peak is the lasin

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FIG. 7. Layout of the FOIL test stand with pumping by a nonmagnetic band lamp.

902Danilov et al.

FIG. 8. Laser pulses of a FOIL set up as in Fig. 7:~a! lasing accompanying photodissociation of C3F7I; ~b! lasing with photodissociation of C3F7I ~1!, lasingaccompanying pumping by a desorption wave of singlet oxygen~2!, luminescence of atomic iodine~3!; ~c! lasing pulses~1, 2, 3! accompanying pumping bya desorption wave of singlet oxygen without changing the working gas.

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determined by the additional pumping by the desorptwave of singlet oxygen. Between them is a time intervalorder of magnitude equal to half the radius of the cell~2.5mm! divided by the speed of sound~about 150 m/sec!.

After this, the pumping was raised to the maximulevel. Figure 8c shows the lasing pulses obtained withchanging the working gas. The first lasing pulse becausthe photodissociation of C3F7I is no longer there, and wehave transferred the origin from which time is measuredthe tenth microsecond. After a certain process of establment of the lasing pulse~in our case this was pulse3, Fig.8c!, the lasing repeated with a weak variation of the puparameters in the course of more than 60 pump pulses.energy of each lasing pulse is about 30 mJ, and the spelasing energy is 0.7 J/L.

Figure 9 shows the layout of the pulsed FOIL as it wset up experimentally. The laser cell, which is 29 mmdiameter, has a fullerene coating on the inner wall. A cenpump lamp 10 mm in diameter, with an interelectrode sping of 600 mm, is located on the axis of the cell. The elecpump energy is 0.6 kJ. After an optimization process,transmittance of the output mirror was 25%. The same figshows the lasing pulses of the FOIL and the luminescepulses of the singlet oxygen. The energy of the lasing puis 360 mJ, and the specific lasing energy is 1.2 J/L. It is hin the first pulse, that the spectral separation of the pumpis implemented: The UV part of the pumping is absorbedthe C3F7I, while the visible part of the pumping passethrough the iodide and is absorbed by the fullerenes ofcoating. The desorption wave of singlet oxygen then emefrom the coating and accomplishes supplementary pumpof the atomic iodine.

CONCLUSIONS

The quantum yield of singlet oxygen in a solution of C60

and O2 in CCl4 with irradiation by a laser pulse (l50.532mm) was about 0.96; in a suspension of FLNs~as-tralenes! and a solution of O2 in CCl4 , it was 0.64.


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Conditions for the release of singlet oxygen into the vpor phase have been found for liquids~the boiling surfaceregime! and for solid-state structures~implementation of agasdynamic desorption wave!.

Preliminary results of the pulsed lasing of a fullereneoxygen–iodine laser using the photodissociation of iodhave been presented. The principle of spectral separatiothe optical pumping was used.

FIG. 9. Layout of FOIL test stand with central lamp pumping.

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*From the materials of a report presented by Professor O. B. Danilov aconference Laser Optics-2003~St. Petersburg, June 30–July 4, 2003!.

1A. A. Artemov, O. B. Danilov, A. S. Grenishin, N. A. Gryznov, V. MKiselev, and A. P. Zhevlakov, ‘‘Pulsed periodic iodine laser,’’ inGasLaser—Recent Developments and Future Prospects, edited by W. Witte-man and V. N. Ochkin~Kluwer Academic Publishers, 1996!, pp 205–220.

2V. Yu. Zalleski�, ‘‘Iodine Laser Pumped by Solar Radiation,’’ Kvant. Elektron. ~Moscow! 10, 1097 ~1983! @Sov. J. Quantum Electron.13, 701~1983!#.

3O. B. Danilov, I. M. Belousova, A. A. Mak, V. Yu. Zalesskiiet al., ‘‘Pos-sibility of realizing fullerene-oxygen-iodine laser with solar pumpin~Sun-Light FOIL!,’’ Proc. SPIE4351, 92 ~2001!.

4O. B. Danilov, I. M. Belousova, A. A. Mak, V. P. Belousovet al., ‘‘On thepossibility of realization the singlet oxygen generation on the base


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optically pumped fullerenes and fullerene-like nanoparticles,’’ inTheFourteenth International Symposium GCL-HPL 2002, Wroclaw, Pola26–30 August, 2002.

5K. M. Gruenewald ‘‘High Power COIL Fiber transmission for D&D application,’’ in The Eleventh Conference on Laser Optics, St. PetersbRussia, June 30–July 4, 2003, Technical Program, p. 17.

6J. W. Arbogast, A. P. Darmanyan, Ch. S. Footeet al., ‘‘Photophysicalproperties of C60 ,’’ J. Chem. Phys.95, 11 ~1991!.

7D. R. Snelling, ‘‘Production of singlet oxygen in the benzene–oxygphotochemical system,’’ Chem. Phys. Lett.2, 346 ~1968!.

8I. M. Belousova, O. B. Danilov, I. A. Sinitsina, and V. V. Spiridonov‘‘Investigation of the optical inhomogeneities of the active substanceCF3I photodissociation laser,’’ Zh. E´ksp. Teor. Fiz.58, 1481~1970! @Sov.

Phys. JETP58, 1482~1970!#.

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Fullerene-oxygen-iodine laser (FOIL) Physical principles