Photo-structural transformation of chalcogenide glasses under non-linear 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 observed 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 reversible darkening is similar to the known effect of photo-structural transformations. It is connected with non-linear excitation to upper intrinsic levels of glass when it exposed to photons with energy less than glass 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 responsible 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.