10 December 2001 How to measure sub-ppm optical homogeneity in fused silica: impact of temperature on accuracy and reproducibility
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Abstract
We report our investigations on interferometric precision measurements of fused silica for a required reproducibility of (sigma) ((Delta) (eta) )<EQ1x10-7 with special focus on thermal environmental conditions. An analytical description is proposed for a qualitative consideration of the thermalization process; numerical results are given for a quantitative prediction of temperature induced measurement errors. Experiments and numerical calculations point to the fact, that, apart from the thermal conductivity, the heat transfer between sample surface and environment has to be taken into account for precise process analysis. Reducing the thickness of the sample, the heat exchange rate between air and glass becomes more important. An effective heat conductivity can be introduced to describe the thermalization process of the sample more easily. Temperature stability of interferometric systems, as well as accuracy and reproducibility of measurement results, were analyzed experimentally in order to study their correlation. The reduction of environmental fluctuations by one magnitude has shown remarkable improvements in the interferometer stability.
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Doerte Schoenfeld, Bodo Kuehn, Armin Steinert, Ralf Takke, "How to measure sub-ppm optical homogeneity in fused silica: impact of temperature on accuracy and reproducibility", Proc. SPIE 4449, Optical Metrology Roadmap for the Semiconductor, Optical, and Data Storage Industries II, (10 December 2001); doi: 10.1117/12.450083; https://doi.org/10.1117/12.450083
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