Two-photon absorption and photoinduced second-harmonic generation in Sb_2Te_3–CaCl_2–PbCl_2 glasses

Abstract

Photoinduced nonlinear optical phenomena in Sb2Te3–CaCl2–PbCl2 glasses have been studied by experimental and theoretical quantum chemistry and molecular dynamics methods. Additionally, photoinduced two-photon absorption (TPA) and second-harmonic generation (SHG) were measured in the IR region from 5.8 to 18 µm. A CO laser (λ=5.5 µm) and parametrically generated wavelengths (5.7–13.4 µm) were used as a source of pump light. With an increase of the photoinducing power, the SHG signal increased for a probe CO2 laser (with double frequency λ=5.7 µm) and achieved its maximum value at a photoinducing power of 1.65 GW/cm2 per pulse. Absolute values of the SHG intensities were more than 1 order of magnitude less than those of χ222 nonlinear optical tensor components for Ag3AsSe3 single crystals. The SHG signal increases strongly for a temperature decrease from 39 to 26 K. Femtosecond probe–pump measurements indicate a SHG maximum at a pump–probe delay time of ∼18 ps. The spectral positions of the TPA maxima depend strongly on the pump power. Differently from the SHG behavior, the TPA results show at least two time-delayed maxima, namely, at 14–17 and 45 ps. These dependencies are explained within the framework of the quantum-chemistry approach, which takes into account photoinduced anharmonic electron–vibration interactions. The Sb–Te tetrahedral plays a key role in the observed photoinduced nonlinear optics effects. The results clearly show that these effects can be used as powerful tools for investigation of picosecond IR nonlinear optics. In addition, these glasses are promising materials for IR femtosecond quantum electronics.