Quest for photo-stable amorphous thin films in ternary Ge_xAs_ySe_100-x-y chalcogenide system is reported. Studied layers were fabricated using pulsed laser deposition technique. Scanning electron microscope with energy dispersive X-ray analyzer, Raman scattering spectroscopy, transmittance measurements, variable angle spectroscopic ellipsometry, and non-linear imaging technique with phase object inside the 4f imaging system were employed to characterize prepared thin films. Their photo-stability/photo-induced phenomena in as-deposited and relaxed states were also investigated, respectively. In linear regime, we found intrinsically photo-stable relaxed layers within Ge₂₀As₂₀Se₆₀ composition. This composition presents also the highest optical damage threshold under non-linear optical conditions.

We present the results of Z-scan measurements (1064 nm, 17 ps) of nonlinear refractive indices and nonlinear absorption coefficients for different compositions of chalcogenide glasses in ${\text{GeS}}_2–{\text{Sb}}_2{\text{S}}_3–\text{CsI}$ system. We show that the simple well known Boling, Glass, and Owyoung model based on the theory of the semiclassical harmonic oscillator can be a useful tool for theoretical predictions of the nonlinear refractive index in these infrared glasses. A quasi-linear behavior is observed relating the nonlinear index and the linear one. Some of the compositions reveal properties potentially useful for all optical switching applications.

We report absolute measurements of the nonlinear refractive index on carbon disulfide (CS2) and fused silica. These materials are commonly used as standard references in nonlinear optical experiments. To obtain more accurate values than those usually used, we have combined the z-scan method inside a 4-f imaging system (in order to analyze the spatial distortion of the diffracted pump beam) with the “Kerr shutter” experiment (to evaluate the temporal pulse width durations for three different wavelengths such as 1064, 532, and 355 nm). We obtained surprisingly n2 values one order of magnitude less than the one usually taken into account in the picosecond regime and a more significant dispersion of the nonlinear refraction index. Experimental and simulated Z-scan transmittance profiles as well as acquired autocorrelation functions in the Kerr-gating experiments are presented here in order to validate our measurements.

In the present work we study the applicability of the binary-encounter-dipole (BED) model and its simpler version the binary-encounter-Bethe model for positron-impact direct ionization. We show that ignoring the exchange and interference effects in the theory of Kim and Rudd [ Phys. Rev. A 50, 3954 (1994)] yields simple analytical formulas with no fitting parameters that can be used to estimate cross sections over a wide energy range except near-threshold region. To correct this deficiency we combine BED theory with the Wannier-type threshold law derived by Klar [ J. Phys. B 14, 4165 (1981)] for positron-impact ionization. We show that such combination is necessary in order to predict cross sections at low positron energies where strong polarization-correlation effects are present during collision and the positronium formation is a dominant scattering process. The present theory is tested for a wide range of targets including helium (He), atomic hydrogen (H), neon (Ne), argon (Ar), molecular hydrogen (${\mathrm{H}}_2$), nitrogen (${\mathrm{N}}_2$), oxygen (${\mathrm{O}}_2$), carbon monoxide (CO), carbon dioxide (${\mathrm{CO}}_2$), and methane (${\mathrm{CH}}_4$). An extensive comparison with available experiments and theories is done.