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Proceedings Paper

Reflective coating for near-infrared immersion gratings
Author(s): Paul J. Kuzmenko; Yuji Ikeda; Naoto Kobayashi; Paul B. Mirkarimi; Jennifer B. Alameda
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Paper Abstract

Achieving high reflectivity from an immersed grating facet can be challenging in the near infrared. The reflectivity of metallic coatings in common use, such as Al and Cr/Au, decrease with decreasing wavelength in the near IR. A layer of copper on ZnSe or ZnS should have a high, immersed reflectivity based on tabulated values of refractive index, but in fact performs poorly. We attribute this to a chemical reaction between the copper and the selenium or sulfur. A non-reactive intermediate layer can prevent this problem. Since reflectivity at an interface increases with increasing difference in refractive index, it is beneficial to choose an intermediate layer of low index. A further improvement is gained by adjusting the layer thickness so that reflections from the two interfaces of the intermediate layer add constructively. We sputtered 130 nm of SiO2 onto ZnSe and ZnS substrates followed by 200 nm of Cu. The copper was then coated with 5 nm of SiC as a protective capping layer. Immersed reflectivity measured shortly after coating exceeded 95% between 1500 and 1100 nm and exceeded 90% down to 850 nm. A repeat measurement after long term exposure to high humidity conditions showed no changes.

Paper Details

Date Published: 13 September 2012
PDF: 11 pages
Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84503O (13 September 2012); doi: 10.1117/12.926668
Show Author Affiliations
Paul J. Kuzmenko, Lawrence Livermore National Lab. (United States)
Yuji Ikeda, Photocoding Inc. (Japan)
Naoto Kobayashi, The Univ. of Tokyo (Japan)
Paul B. Mirkarimi, Lawrence Livermore National Lab. (United States)
Jennifer B. Alameda, Lawrence Livermore National Lab. (United States)


Published in SPIE Proceedings Vol. 8450:
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II
Ramón Navarro; Colin R. Cunningham; Eric Prieto, Editor(s)

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