Negative and positive nonlinear absorption in CdS-doped glasses

. Weinvestigated photodarkend samples, which were exposed to pump light for a long time(about 1 h). Fig.1The optical transmission spectra of the samples studied are shown in Fig. 1. All thesamples are doped by CdS, and different positions of the absorption edge are due tothe different nanocrystal sizes (effect of quantum confinement). We observed negative2