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 stimulated emission spectra evolve in time. We observe individual features corresponding to distinct vibronic resonances in the stimulated emission spectra. The intensities of these features increase subsequent to excitation and persist for hundreds of picoseconds. The fast build-up seen at short delay times is related directly to the vibrational population relaxation time, T1, of the ground vibrational state that is the lower energy state of the stimulated transition. The measured T1 times for perylene vary with both ground vibrational state and solvent. The slow decay rates for these data, the sum of the stimulated and spontaneous decay rates for the particular transition, depend critically on the particular transition that is resonant with the probe laser electric field.