Generation and healing behavior of radiation-induced optical absorption influoride phosphate glasses: The dependence on UV radiation sources and temperature

High purity fluoride phosphate (FP) glasses have a large transmission range from the vacuum ultraviolet to the infrared. They are attractive candidate s for lens systems in microlithography equipment and excimer laser optics. Fluoride single crystals and vitreous silica are well-known traditional mat erials for ultraviolet optics. Crystal sizes are limited and glass is bette r for fabricating optics. For lens systems, a variety of glasses with diffe rent refractive indices and dispersion are required. The UV resonance wavel engths of FP glasses with a low content of phosphate using a two-term Sellm eier dispersion formula are comparable with those of silica and fluoride si ngle crystals. It is known, that UV radiation induces the generation of sev eral defect centers leading to additional absorption bands. The investigati on of the kinetics of defect generation is very important for the predictio n of transmission losses in case of long-time irradiation. To predict the k inetics of defect generation, first the separation of absorption bands is n ecessary. Experiments were carried out using W-lamps, the KrF excimer laser (ns- and fs-pulses) and the ArF excimer laser (ns-pulses). The healing beh avior of radiation-induced absorption bands was investigated using thermal treatment (temperature-dependence) and bleaching experiments (radiation-dep endence). The results of these experiments enable the separation of absorpt ion bands and the-prediction of the defect generation depending on the used radiation source. The healing of strong defects at room temperature is pos tulated to be a diffusion-controlled process. (C) 2001 Elsevier Science B.V . All rights reserved.