Optical Nonlinearities of Glasses Doped with CdS_xSe_1−x

Abstract

Glasses doped with CdS_xSe_l−x microcrystallites, which are normally referred to as color filters, display interesting properties. JAIN and LIND [1] reported degenerate four-wave mixing experiments in these samples and observed 8-nspulse-width limited-decay time for the grating. THOMAZEAU et al. [2] used the optical Kerr effect to measure and time resolve the nonlinearity of lead-silicate glasses on a femtosecond time scale. They measured less than 100-fs response time for the nonlinearity. YAO et al. [3] used pulses of 30-ps duration, and reported free-carrier lifetimes of a few tens of picoseconds. GIBBS et al. [4] observed increasing absorption optical bistability and longitudinal excitation discontinuity in these filters arising from thermal nonlinearity. However, the origin and magnitude of the optical nonlinearity resulting from the electronic processes have not yet been studied carefully in these glasses. In this paper, the results of a pump-probe experiment are reported, and it is concluded that the nonlinearity arises from a bandfilling effect. Furthermore, a novel technique, which employs a modified Twyman-Green interferometer, is used to measure the nonlinear index of a CdS_0.9Se_0.1-doped glass at different wavelengths in the vicinity of the bandgap.