Abstract

The decrease in the quantum yield of 7-diethyl amino-4-methyl coumarin (DAMC) dye with increasing polarity of solvents, is due to their crossover from the intra molecular charge transfer (ICT) state to the twisted intramolecular charge transfer (TICT) state, which radiates extremely weakly.¹ Unlike dialkyl amino benzonitriles which exhibit well resolved ICT and TICT fluorescence in polar solvents,² DAMC exhibits only a single fluorescence band in conventional fluorescence spectroscopy. But under intense pulsed excitation two fully resolved peaks appear in its amplified relative intensities of these two ASE peaks, using nanosecond and picosecond pump pulses. A nitrogen laser producing 300 KW, 6 nsec pulses at 337 nm and a frequency tripled (355 nm), modelocked cavity dumped Nd-YAG laser producing 60 MW, 50 psec pulses served as the nanosecond and picosecond pump sources respectively. The ASE spectra were recorded using a transverse excitation scheme.³ The ASE was fully saturated at the pump powers used in these experiments.

© 1995 IEEE