Abstract
Bicolour illumination by 1.54/0.77 mu m 20 ns pulsed Er:glass laser beams leads to enhancement of the initial effective piezoelectric coefficients for Ag0.5Pb1.75GeS4 and Ag0.5Pb1.75GeS3Se crystals in a different way. The contribution of the photo-thermal effect did not exceed 4 %. The relaxation processes last up to 50 ms and are completely reversible with respect to piezoelectricity. The effect is reproducible even after more than 100 cycles of the photoinduced laser treatment. The use only of the mopnochromatic wavelengths 1.54 mu m (0.77 mu m) did not show sufficient enhancement of the effect, and the changes were commensurable with the background. The efficiency of the laser photoinduced treatment depends on the angle between the bicolour photoinducing beams, ratio of their intensities and their relaxation behaviour is a slightly different. However, at at 50 ms the photoinduced piezoelectric signal disappears for the both samples. It is crucial that laser polarizations of the photoinducing beams do not play important role.