Photoinduced two-photon absorption and second-harmonic generation in As2Te3-CaCl2-PbCl2 glasses

Photoinduced nonlinear optical phenomena in amorphous As2Te3-CaCl2PbCl2 glasses have been studied using experimental and theoretical quantum chemical and molecular-dynamics methods. Especially photoinduced two-photon absorption (TPA) and second-harmonic generation (SHG) were measured in the IR region from 5.5-21 mu m. CO laser (lambda=5.5 mu m) and parametrically generated wavelengths (5.2-13.7 mu m) were used as a source of pumping light. We have found that with an increase of photoinducing power, the SHG for probe CO2 laser (for the double frequency lambda=5.3 mu m) signal increases and achieves its maximum value at photoinducing power 1.45 GW/cm(2) per pulse. The absolute values of the SHG were more than one order less comparing to chi(222) tensor for Ag3AsSe3 single crystals. With decreasing temperature, the SHG signal strongly increases within the 16-24 K temperature range. Femtosecond probe-pump measurements indicate on an existence of SHG maximum at pump-probe time delay about 25 ps. Spectral positions of the TPA maxima are strongly dependent on the pump power. Contrary to the SHG behavior, for the TPA we observe at least two time delayed maxima: at 20-27 and 65 ps. We explain these dependencies within a framework of the quantum chemical approach taken into account with photoinduced anharmonic electron-vibration interaction. We have revealed that As-Te tetrahedra play a key role in the observed photoinduced nonlinear optics effects. The obtained results show that the mentioned effects can be used as a powerful tool for investigations of picosecond LR nonlinear optics processes. Simultaneously the investigated glasses are promising materials for IR femtosecond quantum electronics. [S0163-1829(99)05325-4].