FEMTOSECOND DYNAMICS OF STIMULATED-EMISSION AND PHOTOINDUCED ABSORPTION IN A PPP-TYPE LADDER POLYMER

The dynamics of optical excitations in a PPP-type ladder polymer have been investigated by means of femtosecond pump-probe experiments. Stim ulated emission (SE) is observed around the S-1 --> S-o transition whi le photoinduced absorption (PA) dominates the differential transmissio n at lower energies. The stimulated emission is due to singlet exciton recombination. Comparative studies of the temporal behaviour of the S E and the PA demonstrate that the SE and the PA signals originate from different species. Our results provide evidence that the PA is due to spatially separated electron-hole pairs (indirect excitons).