Laser system for investigation of nonlinear properties of optical materials

An Nd:glass laser system is described that enables smoothly varying the pulse duration of single-frequency laser radiation in the range from 0.2 to 30 ns and focusing the beam to spot sizes from 0.4 mu m at high reproducibility of spectral and spatial-temporal parameters of radiation. This laser system is used to examine the nonlinear photoinduced processes and laser-induced damage in chalcogenide glasses under high-power laser radiation in the near-IR spectral range. It is found that photoinduced losses (absorption and scattering) are produced in chalcogenide glasses by high-power laser radiation with photon energy hv <E-g. The exposure results in both reversible and irreversible structural transformation of these glasses in the exposed region. The reversible darkening is similar to the known effect of photostructural transformations in thin films exposed to photons with energy higher than the glass bandgap. The irreversible contribution is connected with the photoinduced localized destruction of bulk material. It is believed that the process of local destruction is connected with the nonlinear excitation of the structural irregularities randomly distributed in the glass. (C) 1997 Society of Photo-Optical Instrumentation Engineers.