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

Photoinduced nonlinear optical phenomena in amorphous As2Te3-CaCl2PbCl2 gla sses have been studied using experimental and theoretical quantum chemical and molecular-dynamics methods. Especially photoinduced two-photon absorpti on (TPA) and second-harmonic generation (SHG) were measured in the IR regio n 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 hav e 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 achi eves 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(2 22) tensor for Ag3AsSe3 single crystals. With decreasing temperature, the S HG signal strongly increases within the 16-24 K temperature range. Femtosec ond 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 str ongly dependent on the pump power. Contrary to the SHG behavior, for the TP A we observe at least two time delayed maxima: at 20-27 and 65 ps. We expla in these dependencies within a framework of the quantum chemical approach t aken into account with photoinduced anharmonic electron-vibration interacti on. We have revealed that As-Te tetrahedra play a key role in the observed photoinduced nonlinear optics effects. The obtained results show that the m entioned effects can be used as a powerful tool for investigations of picos econd LR nonlinear optics processes. Simultaneously the investigated glasse s are promising materials for IR femtosecond quantum electronics. [S0163-18 29(99)05325-4].