Abstract

CdS_xSe_1-x semiconductor doped glasses are known to darken on intense laser irradiation, the darkening being accompanied by a decrease in the nonlinear refraction coefficient and faster recombination times.¹ We have performed experiments to characterize this darkening in a number of commercial CdS_xSe_1-x glasses. A transmission spectrum (540-820 nm) of the darkened sample indicates that darkening is of a broadband nature. Measurements were made as a function of fluence, repetition rate, and pulse width using a picosecond, frequency doubled Nd:YAG laser. A cw He-Ne laser probe operating at 633 nm was used to monitor the change in transmission during sample irradiation. Darkening was found to increase rapidly during initial stages of laser irradiation and then level off, after which no further change was observed. Darkening was measured at a pulse width of 20 ps for fluences ranging from 4 to 50 mJ/cm². The final extent of darkening is greater for larger fluences, the maximum change in transmission measured being ≃6%. For a given fluence, stronger darkening was produced at a pulse width of 64 ps than at 20 ps while darkening at 64 and 140 ps was approximately the same. This rules out simple excited state or two-photon absorption mechanisms.

© 1989 Optical Society of America