Laser-induced darkening in semiconductor-doped glasses

We have performed experiments to characterize permanent laser-induced darkening in CdS.Sel,- semiconductor-doped glasses with picosecond pulses as a function of fluence, repetition rate, and pulse width. We find that the darkening occurs by means of a nonlinear process that exhibits an anomalous dependence on pulse width. Transmission spectra show that the induced darkening is uniformover the spectral range from the absorption edge out to 820 Am. Darkening in a number of different glasses is compared. On the basis of our results we propose a mechanism that involves photoassistedtrapping of electrons from the semiconductor microcrystallites into states within the glass host material.