Long-term operation of TeO2 acousto-optical device is limited by the formation of surface damage by He-Cd laser irradiation. Similar surface damage occurs by the heat treatment of the TeO2 crystal at 350°C. In this study, TeO2 specimens with various surface treatments have been observed by electron microscopy and X-ray photoelectron spectroscopy. The variation of the transmittance for mechanically polished specimens has been measured in situ during heat treatments. It was found that the thermal surface damage at 350°C was formed in the surface damage layer induced by mechanical polishing. The mechanically 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 UV light irradiation contained Te precipitates with 20 - 40 nm in diameter dispersed in the TeO2 matrix. By the 500°C annealing in air, however, the precipitates disappeared due to the melting, evaporation and oxidation of Te. Based on the results combined with the observation of the surface damage induced by the visible light irradiation, the possible mechanism of the surface damage formation was briefly discussed.
