Phase conjugation and spatial grating formation in amorphous chalcogenide thin films

We present experimental results of phase conjugation (PC) via degenerate four-wave mixing in amorphous Se, Ge10Se90 and Te7Se93 semiconductor thin films. Simultaneously to the PC signal a laser induced grating is formed. However the relief of the grating alone does not seem to explain the experimental results. Measurements of the PC intensity as a function of the film thickness suggest that besides the surface relief, volume effects have to be considered. The PC intensity is measured as a function of the irradiation intensity. The induced gratings are characterized by atomic force microscopy.