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10 June 2004 Mechanisms of radiation-induced defect generation in fused silica
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Excimer laser radiation changes the optical properties of fused silica. These changes include radiation induced absorption and changes of the index of refraction, which in turn determine the expected lifetime of silica lenses used in optical microlithography. A fully automated experimental setup designed for the marathon exposure of samples at low energy densities was employed. Measurements of the induced absorption, of the H2 content using Raman spectroscopy as well as wavefront measurements were performed. A model to predict the aging behavior of silica in optical microlithography systems due to defect generation has been developed for both ArF laser irradiation and KrF laser irradiation. The model includes linear and nonlinear defect generation, relaxation processes and the consumption of hydrogen and describes the radiation induced changes of the index of refraction, the increase as well as the decrease. The model calculations were derived by analytical and numerical methods. A very good agreement in the range of parameters used in the experiments is observed.
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Ute Natura, Oliver Sohr, Rolf Martin, Michael Kahlke, and Gabriele Fasold "Mechanisms of radiation-induced defect generation in fused silica", Proc. SPIE 5273, Laser-Induced Damage in Optical Materials: 2003, (10 June 2004);

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