28 May 2004 CaF2 for DUV lens fabrication: basic material properties and dynamic light-matter interaction
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Lens fabrication for the short wavelengths of the DUV spectral range requires the replacement of glasses, by the crystalline material CaF2. We review mechanism for the interaction of CaF2 with electromagnetic radiation, especially at wavelengths of 193 nm and 157 nm. In the ideal material an absorption process can occur only via a two photon process where charges are separated and an electron--hole pair is created in the material. These excited charges can localize as charge centers or as as localized excitonic state, a bound F--H+-pair. At room temperature all charge centers should recombine within a few pico seconds and no long time change of the optical material properties should be observable. In the real material not only charge center formation but also the stabilization of these charge centers at room temperature due to impurities is identified as a key for the understanding of a radiation induced change of optical material properties.
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Martin Letz, Martin Letz, Axel Engel, Axel Engel, Wolfgang Mannstadt, Wolfgang Mannstadt, Lutz Parthier, Lutz Parthier, Ute Natura, Ute Natura, Konrad Knapp, Konrad Knapp, } "CaF2 for DUV lens fabrication: basic material properties and dynamic light-matter interaction", Proc. SPIE 5377, Optical Microlithography XVII, (28 May 2004); doi: 10.1117/12.536666; https://doi.org/10.1117/12.536666

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