24 July 2014 Enhanced far-ultraviolet reflectance of MgF2 and LiF over-coated Al mirrors
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This paper presents and discuss data obtained on a distribution of Al+MgF2 and Al+LiF witness coupons that show substantial gains in reflectance in the far-ultraviolet (FUV) part of the optical spectrum (90−180 nm). These samples, which have dimensions of 2×2 inches, were coated at various locations inside a 2−me diameter coating chamber at the Goddard Space Flight Center in Greenbelt, MD (USA). These experiments were done to demonstrate a scale−up process for coating up to a 1−m diameter optic, and hence realize the gain in throughput that could be obtained for a telescope system that would employ such mirror coatings. These coatings have been optimized for Lyman-alpha (121.6 nm) or lower wavelengths and they are prepared with the deposition of the MgF2 or LiF layers done at elevated (∼ 250 °C) temperature. These results will be compared to ambient or “cold” depositions. We will also present optical characterization of little-studied rare-earth fluorides, such as GdF3 and LuF3, that exhibit low absorption over a broad wavelength range and could therefore be used as high-index materials to produce dielectric coatings at FUV wavelengths.
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Manuel A. Quijada, Manuel A. Quijada, Javier Del Hoyo, Javier Del Hoyo, Stephen Rice, Stephen Rice, } "Enhanced far-ultraviolet reflectance of MgF2 and LiF over-coated Al mirrors", Proc. SPIE 9144, Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 91444G (24 July 2014); doi: 10.1117/12.2057438; https://doi.org/10.1117/12.2057438


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