Comparison of the influence of the fictive and the annealing temperature on the UV-transmission properties of synthetic fused silica
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and NBOH). Samples with high OH content exhibit gradual recovery from the absorption band within several minutes after exposure to the KrF laser radiation.
The formation of the KrF laser-induced 210 nm absorption band depends on the fictive temperature and on the OH content. Low fictive temperature, as a measure for the number of intrinsic defects, retards E′ generation at the beginning of intense KrF excimer laser irradiation when the majority of defects are generated from precursor defects. However, for longer irradiation periods with pulse numbers of the order of 105 pulses, a high OH content is the beneficial parameter. The accompanying atomic hydrogen is essential for the suppression of the 210 nm absorption band. This happens by transformation of the E′ centers into Si-H defects.
In contrast to a generally held view, annealing (decreasing of the fictive temperature) of fused silica does not always reduce UV induced defect generation. For example, annealing of the samples in an argon atmosphere causes a significantly higher 210 nm absorption increase during KrF excimer laser irradiation (240000 pulses) compared to nonannealed samples.
Two spectroscopic methods to determine the OH content of fused silica were applied: Raman and infrared spectroscopy, which in this work lead to differing results.
The energetics of the 210 nm absorption band generation and bleaching is summarized by a diagram explaining the interaction of the 248 nm laser radiation with fused silica.
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