Abstract

The femtosecond dynamics of hot carriers injected a few LO phonon energies above the bottom of the conduction band are reported. The onset of carrier screening, carrier relaxation, thermalization of the hot electron gas, and electron–hole recombination are extracted from time-resolved absorption spectra. A CPM ring-dye laser amplified to 2 μJ and 100-fs duration with a copper vapor laser at 7.3 kHz is used to generate a white light continuum probe from an ethylene glycol jet. A 750-μm thick sample of a glass doped with ZnSe is pumped at 620 nm. For a zero pump-probe delay, a well-resolved shift of the absorption edge to lower energies is observed, indicating instantaneous onset of carrier screening. At t = +300 fs, the absorption spectra are dominated by a 75-meV blue shift of the absorption edge, signature of complete carrier relaxation, and filling of the bottom of the band.¹ At t = +5 ps the initial recovery of the blue shifted absorption spectra is observed, indicating the onset of electron–hole recombination. The blue shift is almost entirely recovered after 50 ps, with the exception of a small persistent shift which remains for times in excess of several hundred picoseconds. This residual persistent shift is attributed to carriers confined to traps near the bandedge.

© 1986 Optical Society of America