Ultrafast Processes in Spectroscopy 1991

Proceedings of the Seventh International Symposium on Ultrafast Processes in Spectroscopy held in Bayreuth, Germany, 7-10 October 1991

Emil Warburg — Symposium EPS — Meeting

Edited by A Laubereau and A Seilmeier

Institute of Physics Conference Series Number 126 Institute of Physics, Bristol and Philadelphia

Contents

vii Preface

I. Generation of Pico- and Femtosecond Pulses

a) New Mode-Locking Techniques

1-8 Femtosecond laser sources for near-infrared spectroscopy WSibbett

9-14 Femtosecond pulse generation from solid-state lasers Ch Spielmann, F Krausz, Τ Bra bee, Ε Wintner and A J Schmidt

15-18 Coupled cavity mode-locking of a neodymium-doped fiber laser C Unger, G Sargsjan, U Stamm and Μ Müller

19-22 Numerical analysis of pulse formation in solid-state lasers mode-locked with a linear external cavity Μ Müller and U Stamm

23-26 Feedback-controlled mode-locking operation of a Nd:YLF laser at 1.047 μχη Κ Wolf rum and Ρ Heinz

27-30 Antiresonant-ring mirror passive mode-locking of solid state lasers A Agnesi, G Gabetta and G C Reali

31-34 The mode-locking technique using intracavity frequency doubling Κ A Stankov

35-38 Mode-locking of a Nd:YAG laser by a frequency-doubling crystal and saturable absorber Zhen-guo Lü, Qi Wu, Qing-xing Li and Zhen-xin Yu

39-42 Chirped pulse formation in mode-locked solid state lasers with intra­cavity harmonic generation S F Bogdanov, G I Onishchukov, Ρ G Konvisar, S D Ryabko, S R Rustamov and A A Fomichov

43-46 A method for compensating the group-velocity mismatch in the frequency-doubling modelocker Κ A Stankov, V Ρ Tzolov and Μ G Mirkov

47-50 Study of ultrashort pulse generation in a pulsed Nd:YAG laser with an auxiliary nonlinear cavity Zhen-guo Lü, Qi Wu, Qing-xing Li and Zhen-xin Yu

χ Contents

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75-78

79-82

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101-104

b) ThSapphire Lasers and Parametric Oscillators

Femtosecond passively mode-locked Tirsapphire lasers Ρ Georges, Τ Lupine, G Roger and Α Brun

Cavity considerations and intracavity second harmonic generation in Kerr-lens mode-locked titanium-doped sapphire lasers D Georgiev, U Günzel, J Herrmann, V Petrov, U Stamm and K-P Stolberg

Mode-locking of a flashlamp pumped Ti:sapphire laser using the frequency doubling nonlinear mirror Κ Hamal, Κ A Stankov, Η Jelinkova, I Prochazka and Μ Koselja

Generation of ultrashort pulses from the visible to the infrared R Laenen, Η Graener and A Laubereau

Parametric generation of femtosecond pulses by LBO crystal in the near IR S A Akhmanov, IΜ Bayanov, V Μ Gordienko, V A Dyakov, S A Magnitskii, VI Pryalkin and A Ρ Tarasevitch

Picosecond BBO optical parametric oscillator V Kubecek, Y Takagi, Κ Yoshihara and G C Reali

Performance of a barium borate parametric oscillator in the picosecond regime with different cavity configurations G Ρ Banfi, Μ Ghigliazza and Ρ Di Trapani

Multiphoton ionization of atoms with parametrically amplified femtosecond infrared pulses WJoosen, Ρ Agostini, G Petite, J Ρ Chambaret and A Antonetti

c) Dye Lasers

Coherent photon seeding: A scheme for ultra stable ultrashort pulse generation Η Ρ Weber, W Hödel, J Q Bi, Ρ Beaud and D S Peter

Femtosecond pulse generation in a cw pumped passive mode-locked linear rhodamine 6G—DODCl dye laser A Penzkofer and W Bäumler

Prismatic pulse compressor for synchronously pumped mode-locked lasers Κ Osvay, Ζ Bor, A Kovacs, G Szabo, Β Rdczf HA Hazim and Ο Ε Martinez

A simple technique for generation of frequency shifted femtosecond pulses D Grosenick, FNoack, F Seifert and Β Wilhelmi

Ultrashort pulse generation in a DFB-laser with a saturable absorber A A Afanas'ev, Μ VKorol'kov and Τ V Veremeenko

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109-112

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Contents xi

Passively mode-locked dye laser with spatial dispersion in the gain medium Ν Ϊ Michailov

Investigation of chirped pulse amplification in a dye amplifier system Ο Kittelmann, G Korn, J Ringling and F Seifert

d) High Power Lasers

Femtosecond second harmonic generation from A l at the laser intensity level up to 10 1 4 W/cm 2

S V Govorkov, ΝI Koroteev and IL Shu may

Femtosecond x-ray emission from laser irradiated A l targets A Mysyrowicz, J Ρ Chambaret, A Antonetti, Ρ Audebert, J Ρ Geindre and J C Gauthier

First results on the way to a ps multiterawatt glass laser system using fiberless CPA-technique FBillhardt, Ρ Nickles and Ϊ Will

Nonlinear quantum electrodynamics with high power ultrashort laser pulses: possibility of experimental studies Ρ G Kryukov

II. New Techniques and Propagation of Ultrashort Light Pulses

Ultra-sensitive detection with ultra-short pulse ring lasers J-C Diels, Μ Lai and Μ Dennis

Novel laser schemes in gases and vapors pumped by short pulse high power lasers A Tiinnermann, Κ Mossavi and Β Wellegehausen

Ultrafast time-resolved laser scanning microscopy Η Bergner, U Stamm, Κ Hem pel, Μ Kempe, Α Krause and Η Wabnitz

An all solid state picosecond photon counting system for spectroscopy / Prochazka, Κ Hamal, Β Sopko, J Ricka and Μ Hoebel

Best estimates of exponential decay parameters and the design of single-photon-counting experiments Μ Köllner

Three-wave solitons of a new type in Raman scattering of polariton waves A L Ivanov and G S Vygovskii

Spatial and temporal distribution of femtosecond pulses after tight focusing Μ Kempe, U Stamm, R Gutewort, Β Wilhelmi and W Rudolph

xii Contents

163-168 Behaviour of femtosecond pulses in lenses Ζ Bor and Ζ L Horvath

169-171 Propagation-time-dispersion in a streak camera lens Κ Osvay, Ζ Bor, Β Racz and G Szabo

173-180 Ultrafast cross-phase modulation Ρ Heist, J Krüger, W Rudolph, Τ Schröder, Ρ Dorn, F Seifert and Β Wilhelmi

181-184 Study of spectral narrowing for femtosecond pulses propagating in single-mode optical fibres XZhu and W Sibbett

185-188 Bistable solitons J Herrmann and S Gatz

189-192 Coherent effects on soliton amplification in a doped fiber / V MeVnikov and R F Nabiev

193-196 Memory effects assisted phase-conjugation of sub-nano and picosecond pulses in optical fibers ΝI Minkovski and Τ Ρ Mirtchev

III . Coherent Spectroscopy and Nonlinear Optics

197-202 Pressure induced vibrational relaxation in molecular crystals by pico­second coherent Raman spectroscopy in a diamond anvil cell Ε L Chronister and R A Crowell

203-206 Time-resolved investigation of LO-phonon dynamics in semi-insulating and η-type GaAs F Bogani and F Vallee

207-211 Dephasing of excitons in polar semiconductors—The cuprous chloride case F Vallee, F Bogani and C Flytzanis

213-216 Analysis of experimental data on time-domain spectroscopy of molecular gases D V Kolomoitsev and S Yu Nikitin

217-222 Time-domain spectroscopy of molecular vapors with subpicosecond pulses of THz radiation Η Harde and D Grischkowsky

223-226 Two-photon processes with chirped pulses: spectral diffraction and focussing Β Broers, L D Noordam and Η Β van Linden van den Heuvell

227-230 Using of broad-bandwidth stimulated Raman scattering in subpicosecond transient spectroscopy of optical Kerr effect Ρ A Apanasevich, V Ρ Kozich, A I Vodchitz and Β L Kontsevoy

231-234

235-238

239-242

243-246

247-250

251-254

255-260

261-266

267-270

271-274

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279-282

Contents

Third order nonlinear optical properties of substituted poly(p-phenylene vinylene) derivatives Η L Li, S Rentsch and Η Bergner

Four wave mixing processes in strontium vapour generated by tunable femtosecond pulses J Ringling, Ο Kittelmann, F Seifert and J Herrmann

Laser pulses shortening at transient backward SRS and forward scattering suppression R G Zaporozhchenko, IS Zakharova, A V Kachinskii, G G Kotaev and I V Pilipovich

Synchronization of quantum transitions by light pulses: Raman transitions in highly excited hydrogen atom V A Uly bin

Intracavity laser spectroscopy of fast running processes Μ V Pyatakhin

Optical implementation of a Hopfield-type neural network by the use of persistent spectral hole burning media Ο Ollikainen and A Rebane

IV. Applications to Solid State Physics and Surface Dynamics

Femtosecond generation of coherent optical phonons in condensed media Η Kurz

Femtosecond spectroscopy of YBa 2 Cu 3 O v _ 0 : electron-phonon interaction measurement and energy gap observation SVChekalin, V Μ Farztdinov, V V Golovlev, V S Letokhov, Yu Ε Lozovik, Yu A Matveets and A G Stepanov

Investigation of melting processes in GaAs in the femtosecond time domain Τ Schröder, W Rudolph, S Govorkov and I Shumay

Time-resolved spectroscopic investigations of Ti doped YA10 3 and pure YA10 3 crystals Η Chosrovian, S Rentsch and U-WGrummt

Pulsed propagation of luminescence in anthracene Τ Reinot and J Aaviksoo

Photoinjected charge carrier trapping and recombination in one-dimensional conducting polymers / Zozulenko

xiv

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293-298

299-302

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309-312

313-316

317-324

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333-338

339-342

Contents

Ultrafast relaxation of plasma oscillations in Ag islands studied by second-harmonic generation D Steinmüller-Nethl, R Α Höpfel, Ε Gornik, A Lettner and F R Aussen egg

Laser induced electron emission processes of an Au-surface irradiated by single picosecond pulses at λ = 2.94 μτη in the intermediate region between multiphoton and tunneling effects C Toth, G Farkas and Κ L Vodopyanov

V. Applications to Semiconductors

a) Carrier Dynamics in Bulk Semiconductors

Ultrafast electronic and thermal processes in hydrogenated amorphous silicon D Hulin, Ρ Μ Fauchet, R Vanderhaghen, A Mourchid, W L Nighan Jr, J Paye and A Antonetti

Femtosecond spectroscopic study of free carrier induced optical non-linearities in crystalline silicon A Esser} A Ewertz, Τ Zettler, W Kütt and Η Kurz

Picosecond infrared studies of hot holes in germanium W Kaiser, Μ Woerner and Τ Elsaesser

Nonthermalized electron distribution at low density in GaAs DWSnoke, W W Rühle, Y-C Lu and Ε Bauser

Carrier thermalization in GaAs and InP studied by femtosecond luminescence spectroscopy Τ Elsaesser, J Shah, L Rota and Ρ Lugli

Femtosecond nonlinearities and hot-carrier dynamics in GaAs Τ Gong and Ρ Μ Fauchet

Optical nonlinearities at the bandedge of CaAs at room temperature Η Heesel, Τ Zettler, A Ewertz and Η Kurz

Transient reflectivity and transmission spectra of gallium arsenide: dependence on doping and excitation density G Böhne, S Freundt, S Lehmann and R G Ulbrich

Femtosecond relaxation of photoexcited single-species carriers in bulk doped semiconductors G Μ Gale, A Chebira, Ε Fazio and J Chesnoy

Hot carrier relaxation in doped III—V compounds studied by femtosecond luminescence X Q Zhou and Η Kurz

Contents xv

343-344 Reversible gallium arsenide bleaching under the action of picosecond light pulses Ν Ν Ageeva, IL Bronevoi, S Ε Kumekov and V A Mironov

345-348 Theory of hot LO-phonon decay in laser excited direct-gap semiconductors U Wenschuh, Ε Heiner and Κ W Becker

349-352 Dynamic Burstein-Moss effect in InAs at room temperature and passive mode-locking of a 3 μπ\ Er laser Κ L Vodopyanov, Η Graener, C C Phillips and I Τ Ferguson

353-356 Kinetics and relaxation of nonequilibrium electron-hole system in direct gap semiconductors V Dneprovskii, V Klimov and Μ Novikov

357-360 Investigation of carrier temperature relaxation with femtosecond transient grating experiments in CdSxSej_x-semiconductors D van Lap, U Peschel, Η Ε Ponath and W Rudolph

b) Carrier Dynamics in Semiconductors of Low Dimensionality

361-366 Nonlinearity near half-gap in bulk and quantum well GaAs/AlGaAs waveguides Μ Ν Islam, C Ε Soccolich, R Ε Slusher, W S Hobson and A F J Levi

367-370 Resonant electron and hole tunneling between GaAs quantum wells A Ρ Heberle, W W Rühle and Κ Köhler

371-374 Dynamical aspects of pressure induced Γ - Χ electron transfer in a (GaAs) ) 5 / (AlAs) 5 type-I superlattice J Nunnenkamp, Κ Reimann, J Kühl and Κ Ploog

375-378 Hot luminescence and nonlinear effects in shortperiod superlattices under picosecond excitation Ε A Vinogradov, A V Zayats, D Ν Nikogosyan and Yu A Repeyev

379-382 Coulomb relaxation kinetics in a dense quasi-twodimensional electron plasma Κ El-Sayed, Τ Wicht, Η Haug and L Banyai

383-388 An infrared spectrometer for time-resolved intersubband spectroscopy Α Seilmeier, Τ Dahinten, U Plödereder and G Weimann

389-392 Femtosecond relaxation of excited carriers in microcrystallites in a glassy matrix at excitation intensity 10 1 0 -10 1 3 W/cm 2

SVChekalin, V Μ Farztdinov, V V Golovlev, Yu Ε Lozovik, Yu A Matveets, A G Stepanov and A Ρ Yartsev

393-396 Time-resolved studies on the carrier dynamics in quantum dots V Jungnickel, J Puis and F Henneberger

xvi

397-400

401-404

405-410

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419-422

423-426

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Contents

Nonlinear picosecond spectroscopy of zero-dimensional semiconductor V S Dneprovskii, VI Klimov and Ju V Vandyshev

Absorption saturation and nonlinear diffraction of laser pulses in the commercial CdSxSe,_x-doped glasses V A Zaporozhchenko, R G Zaporozhchenko, I V Pilipovich, A Ε Kazachenko and V A Zyulkov

c) Exciton Dynamics

Phase relaxation of excitons in semiconductor mixed crystals U Siegner and Ε Ο Göbel

Subpicosecond spectroscopy of excitons in GaAs/AlGaAs heterostructures Κ Leo, J Shah, S Schmitt-Rink and Κ Köhler

Tunneling versus exciton formation of photo-induced carriers in asymmetric double quantum wells R Strobel, R Eccleston, J Kuhl and Κ Köhler

Exciton relaxation dynamics in GaAs/AlGaAs single quantum well heterostructures Ρ Roussignol, A Vinattieri, L Carraresi, Μ Colocci and C Delalande

The exciton interband scattering and LA-phonon interaction dynamics in GaAs quantum wells R Eccleston, J Kuhl, R Strobel, W W Rühle and Κ Ploog

Carrier-induced shifts of exciton energies in CdTe/CdZnTe superlattices Μ Κ Jackson, D Hulin, J-P Foing, Ν Magnea and Η Mariette

Nonlinear optical response of interacting excitons A L Ivanov, L V Keldysh and V V Panashchenko

Exciton-exciton inelastic collision dynamics in CuBr microcrystals G Tamulaitis, R Baltramiejunas, S Pakalnis and A I Ekimov

d) Opto-Electronics

Ultrafast polarization switching in ridge-waveguide laser diodes A Klehr, Α Bärwolff, R Müller, G Berger, J Sacher, W Elsässer and Ε Ο Göbel

Generation of picosecond pulses by optically pumped short- and ultra-short-cavity semiconductor lasers (theory) Yu D Kalafati and V A Kokin

Picosecond photodetectors fabricated on low temperature GaAs Μ Klingenstein, J Kuhl, R Nötzel, Κ Ploog, J Rosenzweig, C Moglestue, J Schneider, Α Hülsmann and Κ Köhler

Contents xvii

455-456

457-460

461-464

465-470

471-476

477-480

481-484

485-488

489-494

495-498

499-502

503-508

Picosecond optical diagnostic of semiconductors and elements of integrated circuits V V Simanovich, G I Onishchukov and Λ A Fomichev

Investigation of electrical pulse propagation in a n-MOS device by time-resolved laser scanning microscopy Α Krause, Η Bergner, Κ Hempel and U Stamm

Spectral and temporal holography of ultrashort light pulses and its possible applications in opto-electronic systems and devices Yu Τ Mazurenko

VI. Applications to Molecular Systems

a) Ultrafast Photo-Excitation of Molecules

Measurement and conjecture concerning IVR acceleration by methyl group. C H 3 vs C D 3

D Β Moss, C S Pannenter, Τ A Peterson, C J Purse/I and Zhong-Quan Zhao

Infrared transient hole burning with picosecond pulses Η Graener

Resonance interactions of 10 μπ\ picosecond pulses with polyatomic molecules V Μ Gordien ko, ZA Biglov, Ε Ο Dani/ov and VA Slobodyanyuk

Photophysics of the higher excited singlet state of diphenylacetylene V Hirata, Τ Okada, Ν Mataga and Τ Nomoto

Time-resolved optical spectroscopy of donor-acceptor-substituted polyenes G Quapil and Η Port

Nonlinear excited state dynamics of J-aggregates on the femtosecond time-scale R Gagel, R Gadonas and A Laubereau

Ultrafast optical dynamics and nonlinear susceptibility for resonant transitions of excited molecules and aggregates V Bogdanov, S Kulya and Α Spiro

Picosecond relaxation processes in photoexcited metallophthalocyanine aggregates V Butvilas, V Gulbinas and A Urbas

Ultrafast relaxation dynamics of photoexcitations in one-dimensional conjugated polymers Μ Yoshizawa and Τ Kobayashi

x v i i i

509-512

Contents

Ultrafast processes in thiophene oligomers studied by ps absorption measurements D Grebner, Η Chosrovian, S Rentsch and Η Naarmann

b) Solvation Dynamics and Orientational Relaxation

513-518 Classical and quantum solvation Ε Neria, A Nitzan, R Ν Barnett and U Landman

519-522 Solvation dynamics of nile blue studied by time-resolved gain spectroscopy Μ Μ Martin, Ν Dai Hung, L Picard, Ρ Plaza and Υ Η Meyer

523-526 Decay time distribution of fluorescence kinetics in systems with inhomogeneous broadening of electronic spectra D Μ Gakamsky, Ε Ρ Petrov and A Ν Rubinov

527-530 Orientational dynamics of molten 2|Ca(N0 3 ) 2 ] - 3 | K N 0 3 J measured by time-resolved optical Kerr effect Μ Ricci, R Torre, Ρ Foggi and R Righini

531-534 Orientational relaxation dynamics of polar dye probes in n-alkylnitriles G Β Dutt and S Doraiswamy

535-538 Direct observation of femtosecond angular-velocity dynamics in molecular liquids Τ Hat tori, A Terasaki, Τ Kobayashi, Τ Wad a, A Yamada and Η Sasabe

539-542 Direct observation of the orientational motion of small molecules in condensed matter G Seifert and Η Graener

VII. Dynamical Photochemical Processes

543-548 Femtosecond proton and deuterium transfer in aromatic molecules Τ Elsaesser, F Laermer and W Frey

549-552 Intermolecular proton transfer via intramolecular proton transfer: The photodissociation of 2-naphthol-3,6-disulfonate A Masad and D Huppert

553-556 Molecular dynamics study of the picosecond photostimulated conformational dynamics Β A Grishanin, V D Vachev and V Ν Zadkov

557-560 Time-resolved CARS spectroscopy of the series of bisdimethylamino-methine photoisomers W Werncke, Μ Pfeiffer, Α Lau, L Holz and Τ Hasche

561-566 Femtosecond-picosecond laser photolysis studies on photoinduced charge transfer and electron ejection dynamics Ν Malaga, Η Miyasaka and Y Hirata

Contents xix

567—570 Energy transfer phenomena in low and high molecular alkanes Ο Brede and R Hermann

571-574 Analysis of molecular dissociation by a chirped infrared laser pulse Β A Grishanin, V D Vachev and V Ν Zadkov

575—578 Coherence effects on selective ionization of three-level systems driven by pulse sequences of two lasers Κ Johst

579—582 Fast relaxation processes in aromatic free radicals Ν Borisevich, S Melnichuck, S Tikhomirov and G Tolstorozhev

VIII . Applications to Biology

583-588 Femtosecond photoisomerization of rhodopsin as the primary event in vision R W Schoenlein, C V Shank, L A Peteanu and R A Mat hies

589—594 Low temperature reaction dynamics in the primary electron transfer of photosynthetic reaction centers W Zinth, C Lauterwasser and U Finkele

595-598 Femtosecond absorption studies of 14-fluorobacteriorhodopsin Μ Taiji, KBryl, Ν Sekiya, Κ Yoshihara and Τ Kobayashi

599-604 Picosecond time-resolved resonance CARS of bacteriorhodopsin G Η Atkinson and L Ujj

605-608 Primary processes in isolated photosynthetic bacterial reaction centers from ch/oroflexus aurantiacus studied by picosecond fluorescence spectroscopy A R Holzwarth, L Griebenow and Μ G Müller

609-612 Time-resolved fluorescence studies of isolated photosynthetic reaction centers from chloroflexus aurantiacus at low temperatures Μ Hucke, G Schweitzer, Κ Griebenow, Μ G Müller and A R Holzwarth

613-616 Picosecond fluorescence of photosystem I I Dl/D2/cyt b559 and Dl/D2/cyt b559/CP47 pigment-protein complexes Κ Timpmann, A Freiberg, A A Moskalenko and Ν Yu Kuznetsova

617-622 Laserspectroscopic investigations of nonlinear optical effects in molecular aggregates of pigment-protein complexes J Voigt, Th Bittner, G Kehrberg and G Renger

623-626 Aggregation of chlorophyll a in hydrocarbon solution V Helenius, J Erostyak and J Korppi-Tommola

627-630 Energy transfer and charge separation at 15 Κ in membranes of heliobacterium chlorum; temperature dependence of secondary electron transfer Ρ J Μ van Kan and J Amesz

x x Contents

631-634 Femtosecond energy transfer processes in allophycocyanin and C-phycocyanin trimers Ε V Khoroshilov, ί V Kryukov, Ρ G Kryukov, A V Sharkov, Τ Gillbro, R Fischer and Η Scheer

635-638 Photo-activation of a molecular proton crane C J Jalink, A Η Huizer and CA GO Varma

639-642 Fluorescence decay studies of probe molecules distribution throughout the lipid membranes and the determination of 'micropolarity' Ν A Nemkovich, A Ν Rubinov and Μ G Savvidi

643-646 Author Index

647-650 Keyword Index

Inst. Phys. Conf. Ser. No 126: Section VIII Paper presented at Int. Symp. on Ultrafast Processes in Spectroscopy, Bayreuth, 1991

631

Femtosecond energy transfer processes in allophycocyanin and C-phycocyanin trimers

E.V.Khoroshilov, I.V.Kryukov, P.G.Kryukov and A.V.Sharkov P.N.Lebedev Physics Institute, USSR Academy of Science, J17924 Moscow, USSR T.Gilibro Department of Physical Chemistry, University of Umea S-90187 Umea, Sweden R.Fischer and HcScheer Botanisches Institut der Universität München, D-8000 München, FRG

Abstract. Ultrafast processes in C-phycocyanin and allophycocyanin trimers and monomers have been examined by means of polarization pump-probe technique. No femtosecond kinetics was observed in monomelic preparations. The absorption recovery kinetics with t=450±50 fs has been recorded in allophycocyanin trimers. The anisotropy decay kinetics was not obtained in femtosecond time domain. The conclusion about energy transfer between o84 and /?84 chromophores with different absorption spectra was made. The proposed model takes into account a stabilising role of linker peptide. Femtosecond anisotropy decay kinetics was obtained with C-phycocyanin trimers and explained by Förster energy transfer between G84 and /384 chromophores with 65° angle between their orientations.

1. I N T R O D U C T I O N .

Allophycocyanin (APC) and C-Phycocyanin ( C - P C ) are photosynthetic antenna pigments of the light-harvesting complexes (phycobilisomes) of blue green bacteria and red algae. Our knowledge about the energy transfer in the phycobilisome has increased substantially during the last decade, see review works of Glaser (1985) and Holzwarth (1987). Important questions under investigations that still remain open are related to transfer of excitation energy between nearby chromophores in aggregates (mainly trimers) of C - P C and A P C . One has, for instance, to discuss different models for the energy transfer including Förster and excitonic mechanisms. Of special interest is the A P C trimer, since it contains only two kinds of chromophores, namely a&A and /384 ones. The optical spectrum of the A P C monomer has the maximum at 620 nm. In contrast to this, the spectrum of A P C trimer has a sharp peak at 650 nm and a shoulder about 620 nm. In contrast to A P C , C-phycocyanin monomer contains three chromophores, 084, ß&4 and /3l55, and absorption spectrum of the C - P C trimer with maximum near 620 nm shows close resemblance to that of the C - P C monomers.

The picosecond pump-probe technique has been applied to A P C and C - P C monomers and trimers to investigate the excitation energy transfer ( Sandström ct al. (1988), Gillbro ct al. (1988), Beck et al. (1990)). One can expect the fastest energy transfer processes between o84 and /?84, which form three small distance pairs upon formation of A P C and C - P C trimers. The information about orientation of C - P C chromophores and distances between them (Schirmcr ct al., 1987), makes it possible to estimate rates of energy transfer processes in this pigment. We have examined the ultrafast processes in C - P C and A P C monomers and trimers with femtosecond time resolution. Preliminary results obtained with A P C were published in previous communication of Khoroshilov et al. (1991).

© 1992 IOP Publishing Ltd

632 Ultrafast Processes in Spectroscopy 1991

2 . M A T E R I A L S A N D M E T H O D S

The A P C and C - P C trimers were isolated from Masiigosladus laminosus. We used two kinds of A P C trimeric preparations. The absorption spectrum of the first one (Sample No 1) is very close ίο the spectrum of A P C complex with 8.9 kD linker peptide (Holzwarth et al.,1990). The spectrum of the second preparation (Sample No 2) similar to the spectrum free of linker peptide A P C with higher shoulder absorption. A P C and C - P C monomers were obtained by adding, respectively, K S C N and NaSCN to 1.2 Μ directly before measurements. The measurements were made at 20° C in a rotating cell of 1 mm optical path length. A 70-femtosecond pulses at 615 nm from CPM-laser were amplified at 10 kHz repetition rate in the multipass jet amplifier (Kryukov et al.,1988) and served both for pumping and probing. A pump-probe absorption measurements were made with polarization of probe pulse parallel or perpendicular to the polarization of the exciting pulse, and photoinduced anisotropy was calculated according to the standard formula.

3. R E S U L T S

Figure 1 shows the photoinduced optical density changes measured with the first A P C preparation and Fig.2 exhibits results for the second A P C sample. For both samples we have obtained 4 5 0 ± 5 0 fs decay of the initial bleaching for both polarizations of a probing pulse. The photoinduced anisotropy is 0 . 4 ± 0 . 1 for the first sample and 0 . 3 7 ± 0 . 0 3 for the second one within two picoseconds after the excitation The anisotropy decay was not observed during this period. The main difference between two results is that for the second sample the rest bleaching measured after femtosecond decay is more than half of the bleaching measured immediately after the excitation, but approximately complete absorption recovery was observed for the first sample.

Figure 3 shows the optical density changes measured with trimers of C - P C within 1 ps period after the excitation. One can see the similar to A P C femtosecond absorption recovery at parallel polarization of probing pulse and only the initial bleaching without any femtosecond recovery kinetics at perpendicular polarization. The anisotropy, calculated from experimental data, obtained within 5 ps, is shown in Fig.4. Immediately after the excitation the anisotropy is equal to 0.4 and decays to the level of 0 . 2 3 ± 0 . 0 2 . The anisotropy decay has 0.5+0.1 ps lifetime using one-exponential fitting (dashed line).

Figure 1. Absorption recovery of allophycocyanin trimers at 615 nm (Sample No 1) measured with probe pulse polarization parallel (solid line) and perpendicular (dashed line) to the exciting pulse.

Figure 2. Absorption recovery of A P C trimers at 615 nm (Sample No 2) with probe pulse polarization parallel (solid line) and perpendicular (dashed line) to the exciting pulse.

Applications to Biology 633

0.0 '—L

C - P C - t r imer

_1 I 1 I I I L

0.1 0.3 0.5 0.7 t ime.ps

0.9 1.1 1.3

C - PC - ir imei

0.4 1.2 2.0 2.8 3.6 4 .4 t ime.ps

Figure 3. Absorption recovery of C-phycocyanin trimers at 615 nm with probe pulse polarization parallel (solid line) and perpendicular (dashed line) to the exciting pulse.

Figure 4. Anisotropy calculated for C - P C at 615 nm according to formula r ( t ) = ( M n - M | ) / (ΔΑ| |+2ΔΑΙ) (solid line) and one-exponential fitting with 0.5 ps lifetime (dashed line).

No evident femtosecond kinetics was observed with A P C and C - P C monomers within two picoseconds after the excitation for both polarizations of the probing pulse.

4. D I S C U S S I O N

We can conclude from the experimental results that femtosecond processes take piace only in APC and C - P C trimeric prepapations. We attribute the observed kinetics to energy transfer processes between adjacent a84 and ßS4 chromophores in trimers. The results obtained with C -PC trimers are in a good agreement with Förster energy transfer calculations (Sauer and Scheer,l988) based on X-ray crystal structure data of Schirmer et al.(1987). .The lifetime of the experimentally observed anisotropy decay is determined by the sum of rate constants of direct (G84 -+ßS4) and back (ß&4 -* C$4) energy transfer reactions. The rate constants were estimated by Sauer and Schecr (1988) from the distance between chromophores and their orientations and also from the absorption spectra of the individual chromophores published by Sauer et al.(1987). This sum is 3039 ns _ 1 for M.laminosus and corresponds to 330-fs kinetics. This kinetics is faster than depicted in Fig.4 using one-exponential fitting. But taking into account that 30-ps energy transfer processes were measured by Sandström et al.< 1988) and calculated by Sauer and Schecr (1988) for C - P C trimers (ßi55-*ß%4 process), it is possiplc to describe the experimentally observed anisotropy decay by two-exponential fitting with ti «0.33ps and t2 -30ps. The final anisotropy , which was obtained when the equilibrium between C&4 and ß&4 has been reached, depends on the angle between these two chromophores. Taking 65° for this angle (Schirmer ct al.,1987) and using absorption cross sections of o84, ß&4 and ß\55 chromophores at 615 nm and

634 Ultrafast Processes in Spectroscopy 1991

Β

Figure 5. A model for fast energy transfer pathways in intact trimers (A) and in partly disintegreted trimers (B).

rate constants for direct and back reactions, we calculated the final anisotropy as 0.225 which is in agreement with the experimentally obtained value.

The explanation of the fast isotropic decay in A P C trimers, which is not accompanied by a change of the anisotropy, would be a transfer of energy from a chromophore (a84 or ßS4) absorbing at 615 nm to another chromophore absorbing at 650 nm. Upon aggregation of monomers into trimers only one of the chromophores acquires a strongly red-shifted spectrum with maximum at 650 nm because of the new chromophore surrounding, while the other one might contribute to the shoulder at 620 nm. If the absorption of the 650-nm chromophore contributes negligibly to the absorption at 615 nm, one would expect no change in anisotropy during the energy transfer, but a complete recovery of the ground state absorption at 615 nm as the excited 615-nm chromophore transfers its energy to the other chromophore. This situation was realised with the first A P C trimeric preparation and is described by the energy transfer scheme with C3 -symmetry (Fig.5a). To explain the rest optical density changes obtained with the second A P C preparation we invoked trimer heterogeneity (Fig.5b). This heterogeneity, probably, deals with the partial desintegration of the Sample No 2 because of the loss of the stabilizing role of linker peptide. As a result, the distance between donor and acceptor in one of three pairs is increased, and acceptor (Α') acquires 620-nm spectrum instead of 650-nm one of another acceptors (A). This leads to the increasing of the absorption in 620-nm shoulder of the spectrum free of linker peptide A P C . Excited at 615 nm donor D (or acceptor A') of this pair transfers its energy in picosecond time domain, and the rest bleaching, observed after femtosecond kinetics, is due to these chromophores in the excited state.

R E F E R E N C E S

Beck W . F . , Dereczeny M., Yan X. and Sauer Κ. 1990 Ultrafast Phenomena YII (SpringenBerlin) pp. 535-537

Gillbro T.,Sandstro*m Α., Swndström V. , Fischer R. and Scheer.H. 1988 Light-Harvesting Systems (Berlin: Walter de Greuter & Co) pp.457-467

Glaser A. 1985 Annu. Rev. Biophys. Biophys.Chem. 14, 47 Holzwarth A.R. 1987 Top Photosynth. 8,95 Holzwarth A.R. , Bittersmann Ε., Reuter W. and Wehrmeyer W. 1990 Biophys.J. 57,133 Khoroshilov E . V . , Kryukov I .V. , Kryukov P . G . , Sharkov A.V. and Gillbro T . 1991 Laser

Applications in Life Sciences, Proc.SPIE 1403 pp. 431-433 Kryukov I .V . , Kryukov P .G. , Khoroshilov E . V . and Sharkov A.V. 1988 SovJ. Quantum Electron.

18, 830 Sauer Κ., Scheer Η. and Sauer P. 1987 Photochem. Phoiobiol 46, 427 Sauer Κ. and Scheer H. 1988 Biochim. Biophys Acta 936,157 Schirmer T . , Bode W. and Huber R. 1987 / . Mol Biol 196, 677 Sflndstrom Α., Gillbro T . , Sundström V., Fischer R. and Scheer H. 1988 Biochim. Biophys. Acta 933,42