OPTICAL NONLINEARITY AND FAST SWITCHING DUE TO BIREFRINGENCE AND MODE-COUPLING IN CDS CRYSTALS

Interference and mode coupling between ordinary and extraordinary waves lead in non-isotropic media to a rotation of the plane of polarization of the transmitted light. Placing the specimen between two polarizers, pronounced interference patterns are observed near the isotropic point. Pump and probe experiments with donor doped and undoped CdS crystals demonstrate for the first time a fast blue shift of the interference spectra by the action of intense laser light pulses. This gives rise to a nonlinear optical switching in the ns region. The induced change of the transmission due to saturation effects of the donors leads to a change of the birefringence DELTA-n = n parallel-to - n perpendicular-to. Under ps excitation, very fast rotations of the plane of polarization have been observed. Coherent phenomena like two photon absorption or the optical induced Stark effect are apparently responsible for relaxation processes with decay times in the sub-ps region.