Abstract

We report on the dynamics of nonequilibrium distributions of dye molecules, such as, Nile Blue, Cresyl Violet, sulforhodamine 640, and rhodamine B, excited by pump pulses of 65-fs duration and probed by pulses compressed to durations of 10 fs. We examine a spectral region centered at the pump wavelength, 618 nm, and ranging from 570 to 670 nm. Differential absorption spectra are taken at intervals of 25 fs following the initial excitation of the dye. We observe optically induced changes which reach equilibrium within a few hundred femtoseconds following excitation. Of special interest is hole burning at the pump wave-length as well as bleaching of replica holes at energies shifted from the pump energy by a vibrational quantum energy. We also observe transient excited state absorption in near-infrared dyes due to pump-induced nonequilibrium population of the vibrational levels of the upper electronic state and transient-induced transmission in dyes such as rhodamine B where our 618-nm pump pulse lies below the absorption edge of the dye. We discuss the relationship of these optically induced dynamics with ultrashort pulse formation in lasers.

© 1986 Optical Society of America