Stimulated resonance Raman scattering from single crystals of a thiophene/phenylene co-oligomer

We have investigated the stimulated resonance Raman scattering from single crystals of a thiophene/phenylene co-oligomer. The very narrow lines [full width at half maximum (FWHM)=11-20 cm(-1)] are observed in the same spectral regions where the spectrally narrowed emissions (FWHMapproximate to300 cm(-1)) occur upon excitation with intense laser pulse. We related these modes to the stimulated resonance Raman scattering. Two lines of Raman shifts of 1466 and 1605 cm(-1) are of molecular origin. Another line with an energy shift of similar to1260 cm(-1) from excitation energy, on the other hand, implies the presence of the coherence of crystal origin. The associated split lines accompanying this mode are thought to constitute the longitudinal modes in the Fabry-Perot cavity naturally formed in the crystals. (C) 2003 American Institute of Physics.