LASER SYSTEM FOR INVESTIGATION OF NONLINEAR PROPERTIES OF OPTICAL-MATERIALS

An Nd:glass laser system is described that enables smoothly varying th e 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 hig h reproducibility of spectral and spatial-temporal parameters of radia tion. 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 chalco genide 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 transform ations in thin films exposed to photons with energy higher than the gl ass bandgap. The irreversible contribution is connected with the photo induced localized destruction of bulk material. It is believed that th e process of local destruction is connected with the nonlinear excitat ion of the structural irregularities randomly distributed in the glass . (C) 1997 Society of Photo-Optical Instrumentation Engineers.