Abstract :
Summary form only given. Ultrafast nonlinear optical responses in photoexcitations in polydiacetylenes (PDAs), and substituted polyacetylene (PA) were investigated. The decay kinetics in PDAs and PTs are discussed in terms of the /sup 1/B/sub u/ exciton, /sup 1/A/sub 9/ exciton, free and self-trapped excitons (STE) and biexciton, while the relaxation in the substituted PA is explained by the confinement effect of soliton-antisoliton pairs. Optical Stark shift in the Raman gain spectrum was observed for a single crystal of polydiacetylene (PDA), PDA-DFMP (2,5-bis(trifluoromethylphenyl) PDA) by using pump-probe spectroscopy apparatus based on a femtosecond CPM laser. The femtosecond time-resolved Raman gain spectra of PDA-3BCMU were measured using two pump pulses at 1.97 eV and 1.78 eV. The spectra at various delay times between -500 fs and 1 ps are explained in terms of the conformational change due to the geometrical relaxation taking place from acetylene-type to butatriene-type configuration associated with the self trapping of free exciton followed, by quasi-thermalization with time constant shorter than 200 fs, which is consistent with the formation time constant of the quasithermal self-trapped exciton being 140 fs determined by the absorption spectral change.
