GAIN DYNAMICS IN CONJUGATED POLYMERS AT ROOM-TEMPERATURE

We report on stimulated emission and optical gain in BEH-PPV polymer f ilms at room temperature. Performing femtosecond Dump-probe experiment s we find very fast (less than or equal to 100 fs) relaxation of excit ons within a ladder of vibronic states. From spectra taken at very ear ly times after photoexcitation we identify several vibronic transition s with a linewidth of about 8 nm. Strong coupling of excitons to these vibrations leads to stimulated emission and large optical gain of up to 10(4) cm(-1). For a pump-probe delay of 200 fs the different transi tions are no longer distinguishable due to broadening through spectral diffusion and exciton migration. The lifetime of the optical gain cor responds to the exciton lifetime. Population depletion by stimulated e mission leads to a density dependent decay within a few hundred fs up to about 2 ps.