Photoinduced effects in the Sb2Se3-BaCl2-PbCl2 glasses

Photoinduced optical phenomena in amorphous Sb2Se3-BaCl2-PbCl2 glasses are studied using experimental spectroscopic and theoretical quantum chemical methods. Photoinduced two-photon absorption (TPA) (for lambda = 10.6 mu m) and second harmonic generation (SHG) (for the output wavelengths 5.3 mu m) were measured. CO laser (lambda = 5.5 mu m) was used as a source of photoinducing light. We have found that with an increasing CO-laser exposure the SHG maximum output signal increases and achieves its maximum value at CO photon fluence 18 x 10(13) phot./cm(2) per pulse after two hours of illumination. The output SHG signal was more than one order less comparing with ZnS crystals in case of its third rank nonlinear optical susceptibility tensor components chi(222) (lambda = 10.6 mu m). With decreasing temperature the SHG signal strongly increases within the 26-32 K temperature range. Time-dependent probe-pump measurements show an existence of SHG maximum at time delay about 45 ps. Good correlation between SHG and TPA was observed. Spectral positions of the TPA maxima strongly depend on the photoinducing power. We observed at least two maxima of the TPA: at 26 and 70 ps. We explain this dependence within a framework of the quantum chemical approach taken into account electron-vibration anharmonicity. Coming out from the performed calculations and infrared (IR)-spectroscopy Fourier technique measurements in the spectral region between 100 and 300 cm(-1) we have ascertained a key role of Sb-Se fragments in the observed photoinduced effects. We have also compared different existing models of the photoinduced changes. The studied glasses have relatively low nonuniformity through the sample surfaces and can be used as a promising material for picosecond IR laser devices. (C) 1999 American Institute of Physics. [S0021-8979(99)03901-8].