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26 September 1997 Ultrafast relaxation of fullerenes and fullerites by broadband femtosecond laser spectrometry
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Proceedings Volume 3239, Photon Echo and Coherent Spectroscopy; (1997)
Event: PECS '97: Photon Echo and Coherent Spectroscopy, 1997, Yoshkar-Ola, Russian Federation
Relaxation of fullerenes in solids and solutions was investigated by femtosecond pump-probe technique at various experimental setups. Intensity of excitation pulse was varied at 1010 - 1012 W/cm2, energies of pump and probe quanta were changed from 1.57 to 3.14 eV, pulse duration -- from 60 to 350 fs. An increase of absorption was observed in solutions with a time scale of 1.2 ps for C60 and 0.15 ps for C70 after excitation of HOMO-LUMO transition. It was attributed to symmetry breaking of excited molecules. Observed for solid C60 dependence of relaxation rate on the density of excited molecules and on the wavelengths of the pump and probe pulses is explained by 'hot' singlet-singlet annihilation the rate of which is proportional to R-3. Comparison of photoinduced absorption and bleaching decays allowed to conclude that only a small fracture of excited molecules produce localized charge carriers, mainly by excitonic annihilation proces and these carriers are responsible for long-lived residual absorption observed in photoinduced absorption kinetics. Difference absorption spectra observed near zero delay time were similar to electroabsorption ones superimposed on excited state absorption of C60 film. This electroabsorption feature disappeared in phase with pumping pulse. This phenomenon is connected with Stark shift in strong electric field of the powerful pumping pulse.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Daniel Boucher, Sergey V. Chekalin, S. A. Kovalenko, Juru A. Matveets, P. Masselin, M. G. Novikov, V. V. Ragulsky, and Andrei G. Stepanov "Ultrafast relaxation of fullerenes and fullerites by broadband femtosecond laser spectrometry", Proc. SPIE 3239, Photon Echo and Coherent Spectroscopy, (26 September 1997);

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