Modeling of excimer laser radiation induced defect generation in fluoride phosphate glasses

Fluoride phosphate (FP) glasses with low phosphate content are high-transpa rent in the deep ultraviolet (UV) range and attractive candidates for UV-op tics. Their optical properties are complementary to fluoride crystals. The anomalous partial dispersion makes them desirable for optical lens designs to reduce the secondary spectrum. Their UV transmission is limited by trace impurities introduced by raw materials and decreases when exposed to W-rad iation (lamps, lasers). The experiments of the paper published previously i n this journal were used in order to separate radiation induced absorption bands in the fluoride phosphate glass FP10. In this paper the generation me chanism of the phosphorus-oxygen related hole center POHC2 is investigated in detail in glasses of various compositions (various phosphate and impurit y contents) in order to predict the transmission loss in case of long-time irradiation. Experiments were carried out using ArF- and KrF-excimer lasers (ns-pulses). POHC2 generation strongly depends on the phosphate content an d on the content of Pb2+. A model was developed on these terms. Rate equati ons are formulated, incorporating the influence of the Pb2+-content on the defect generation, a two-step creation term including an energy transfer pr ocess and a one-photon bleaching term. This results in a set of coupled non linear differential equations. Absorption coefficients and lifetimes of the excited states were calculated as well. Experimental results compared well with the numerical analysis of the theoretical rate equations. (C) 2001 El sevier Science B.V. All rights reserved.