22 January 2004 Grating efficiencies comparison study: calculations versus metrology for various types of high groove density gratings at VUV-UV wavelengths
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Abstract
The complex study of a ultra-fine (4000 to 5870 grooves/mm) holographic gratings designed for Near Ultra Violet (NUV) channel of Cosmic Origin Spectrograph (COS) are presented. The gratings underwent a comprehensive program of efficiency and scatter characterization at flight-like environment conditions. Initial tests revealed significant departures of grating efficiencies from the values predicted. Effects of profile non-replication (layers nonconformity) for multi-layer coated grating surfaces are investigated. The rigorous efficiency modeling based on groove profiling atomic force microscopy (AFM) data for both multi-layer conformal and non-conformal coated gratings in both polarizations allowed to identify the problem as a leaky mode anomalies for dielectrically coated gratings. Both shift in peak efficiencies and wide absorption band are observed to be critically dependant of grating groove shape and reflective coating thickness. Grating depth/profile topography changes induced by coating process are observed and called for groove profile measurements at all stages of the gratings production line. Grating scatter characterizations data for COS and SORCE/SOLSTICE gratings at UV-VUV wavelength are presented. The wavelength scaling at VUV-UV waveband (140 nm to 442 nm) for holographically ruled 3600 gr/mm grating are also reported.
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Ivan G. Kuznetsov, Erik Wilkinson, David A. Content, Rene A. Boucarut, Timothy J. Madison, "Grating efficiencies comparison study: calculations versus metrology for various types of high groove density gratings at VUV-UV wavelengths", Proc. SPIE 5178, Optical Modeling and Performance Predictions, (22 January 2004); doi: 10.1117/12.507946; https://doi.org/10.1117/12.507946
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