IR-stimulated second harmonic generation in Sb2Te2Se-BaF2-PbCl2 glasses

Theoretically predicted and experimentally observed infrared-induced second-harmonic generation of glasses in the mid-infrared spectral region can be described by fifth-order nonlinear optical susceptibility. The effect is observed in the mid-IR region when the value of the electronic energy gap is comparable to the energies of actual phonons participating in the anharmonic (non-centrosymmetric) electron -phonon interactions. As subjects for investigation, chalcohalide Sb2Te2Se-BaF2-PbCl2 glasses were chosen. They are transparent, over a spectral range of 1.1 - 10.9 mum. The second-harmonic generation (SHG) output signal within the 1.5 - 4.8 mum spectral range has significant spectral dependence. Correlation of the SHG spectral maxima positions with spectral positions of anharmonic phonon frequencies confirms that the fifth-order steady-state process occurs due to cascading processes and IR-induced charge density non-centrosymmetry. A maximum value of the SHG is achieved at a pump-probe delay time of 18 - 36 ps, which is typical for anharmonic electron - phonon interactions. As temperature rises, the values of the photoinduced SHG signal susceptibility increases up to 3 x 10(-39) m(4)/ V-4. The SHG signal reaches a saturation point for the IR-pump power densities of about 0.8 GW/cm(2), which corresponds to the output SHG intensities of about 6 x 10(-4) with respect to fundamental one. The values of the diagonal fifth-order tensor component chi(xxxxx)((2omega)) are at least one order of magnitude larger than the off-diagonal tensor components.