Abstract: Changes in the transmission of commercially available semiconductor doped glasses and porous silicon layers are studied by using picosecond pump and probe measurements. Bleaching bands attributed to the saturation of optical transitions in semiconductor nanostructures (crystallites or wires) are registered in time-resolved differential transmission spectra for both of the materials under investigation. It is found that porous silicon exhibits strong and fast optical nonlinearity (third-order nonlinear susceptibility is about 10$+$MIN@8$/ esu; transmission recovery time is 30-40 ps) which can be used for optical switching. !29
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