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 m ethods. Photoinduced two-photon absorption (TPA) (for lambda = 10.6 mu m) a nd second harmonic generation (SHG) (for the output wavelengths 5.3 mu m) w ere measured. CO laser (lambda = 5.5 mu m) was used as a source of photoind ucing light. We have found that with an increasing CO-laser exposure the SH G maximum output signal increases and achieves its maximum value at CO phot on fluence 18 x 10(13) phot./cm(2) per pulse after two hours of illuminatio n. The output SHG signal was more than one order less comparing with ZnS cr ystals in case of its third rank nonlinear optical susceptibility tensor co mponents chi(222) (lambda = 10.6 mu m). With decreasing temperature the SHG signal strongly increases within the 26-32 K temperature range. Time-depen dent probe-pump measurements show an existence of SHG maximum at time delay about 45 ps. Good correlation between SHG and TPA was observed. Spectral p ositions of the TPA maxima strongly depend on the photoinducing power. We o bserved at least two maxima of the TPA: at 26 and 70 ps. We explain this de pendence within a framework of the quantum chemical approach taken into acc ount electron-vibration anharmonicity. Coming out from the performed calcul ations 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 compa red different existing models of the photoinduced changes. The studied glas ses have relatively low nonuniformity through the sample surfaces and can b e used as a promising material for picosecond IR laser devices. (C) 1999 Am erican Institute of Physics. [S0021-8979(99)03901-8].