NONLINEAR-OPTICAL SWITCHING FRONTS IN CDS

Nonlinear impurity-related optical switching at low temperatures was f ound in CdS at moderate illumination intensities. A theoretical analys is of this effect based on the bleaching of ionized acceptor states is performed with the help of generation-recombination kinetics and trav elling field equations. We demonstrate by numerical simulation that th e optical switching process involves a switching front that propagates from the front facet where the exciting laser light enters the crysta l to the far end of the crystal. Experimental evidence for our theoret ical prediction is presented. The experimental results were obtained w ith the help of a pump-and-probe experiment where the probe was perpen dicular to the pump and placed at various positions along the crystal. The results show a clear dependence of the onset of the transmitted p ulse with regard to the onset of the pump pulse on the position of the probe along the crystal. Problems associated with the experiment, i.e . that the results could only be obtained for a narrow regime of (temp oral) mean pump intensities, are discussed.