PHOTO-STRUCTURAL TRANSFORMATION OF CHALCOGENIDE GLASSES UNDER NONLINEAR ABSORPTION OF LASER-RADIATION

The optical properties of commercial and experimental arsenic sulfide glasses were studied during and after exposure to pulsed Nd:YAG laser radiation at 1.064 and 1.318 mu m Photo-induced losses (absorption and scattering) are produced in chalcogenide glasses by high-power laser radiation, the with photon energy hv < E-g. This phenomena is only obs erved if the irradiance is greater than a value of about 10(8) W/cm(2) . Such exposure results in both reversible and irreversible structural transformations of these glasses in the exposed region. The reversibl e darkening is similar to the known effect of photo-structural transfo rmations. It is connected with non-linear excitation to upper intrinsi c levels of glass when it exposed to photons with energy less than gla ss bandgap. The irreversible contribution is due to the photo-induced localized destruction of bulk material, which is nor completely erased by annealing near the glass transition temperature. Damage sites an r esponsible for absorption and scattering in this case. It is believed that a process of laser damage is caused by the thermal instability of structural irregularities randomly distributed in glass, which absorb laser radiation.