ULTRAFAST STIMULATED-EMISSION SPECTROSCOPY OF PERYLENE IN DILUTE-SOLUTION - MEASUREMENT OF GROUND-STATE VIBRATIONAL POPULATION RELAXATION

We report ultrafast stimulated emission measurements of perylene in a series of polar and nonpolar solvents. In all solvents the perylene st imulated emission spectra evolve in time. We observe individual featur es corresponding to distinct vibronic resonances in the stimulated emi ssion spectra. The intensities of these features increase subsequent t o excitation and persist for hundreds of picoseconds. The fast build-u p seen at short delay times is related directly to the vibrational pop ulation relaxation time, T1, of the ground vibrational state that is t he lower energy state of the stimulated transition. The measured T1 ti mes for perylene vary with both ground vibrational state and solvent. The slow decay rates for these data, the sum of the stimulated and spo ntaneous decay rates for the particular transition, depend critically on the particular transition that is resonant with the probe laser ele ctric field.