THERMAL AND PHOTOINDUCED SURFACE DAMAGE IN PARATELLURITE

Long-term operation of TeO2 acousto-optical device is limited by the f ormation of surface damage caused by the He Cd laser irradiation. Simi lar surface damage occurs during the heat treatment of the TeO2 crysta l at 350 degrees C. In this study, TeO2 specimens after various surfac e treatments have been observed by electron microscopy and X-ray photo electron spectroscopy. The variation of the transmittance for mechanic ally polished specimens has been measured in situ during heat treatmen ts. It was found that the thermal surface damage at 350 degrees C was formed in the surface layer damaged by mechanical polishing. The mecha nically damaged layer was amorphous and deficient in oxygen in the as- polished state. The electron microscopic observation revealed that the surface damage layer induced by heat treatments or by the ultraviolet light irradiation contained tellurium particles (20-40 nm) in diamete r dispersed in the TeO2 matrix. On annealing the TeO2 specimen at 500 degrees C in air, however, the particles disappeared because of the me lting, evaporation and oxidation of tellurium which restores the trans mittance of the crystal. Based on the results, combined with the obser vation of surface damage induced by the visible light irradiation, a p ossible mechanism of the surface damage formation has been briefly dis cussed.