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Au coatings for spaced based reflectors

: Schwinde, Stefan; Shestaeva, Svetlana; Stempfhuber, Sven; Lukowicz, Henrik von; Kuhnhenn, Jochen; Schröder, Sven

Volltext ()

Cugny, B. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
International Conference on Space Optics, ICSO 2020 : Virtual Conference, 20 March - 2 April 2021
Bellingham, WA: SPIE, 2021 (Proceedings of SPIE 11852)
Paper 118521Q, 8 S.
International Conference on Space Optics (ICSO 2020) <2021, Online>
Konferenzbeitrag, Elektronische Publikation
Fraunhofer INT ()
Fraunhofer IOF ()
gold; coating; sputtering; reflector; Interdiffusion; radiation; durability; GALA

Gold shows a very high reflectivity in the IR range. In addition, Au (and protected Au) is more robust than Ag (and protected Ag). Therefore, Au based coatings are of high interest. Common techniques for the deposition of optical Au coatings are sputtering and evaporation. In this contribution, both techniques, sputtering and evaporation, as well as unprotected and protected Au will be considered. A comparison of reflectivity between sputtered and evaporated Au-layers shows a slightly higher reflectivity for evaporated Au. Beside reflectivity after coating, decrease of reflectivity due to interdiffusion at increased temperatures (250°C) between adhesion layer and the reflective Au-layer is considered. In case of space-based applications, interdiffusion in thin film coatings could be activated due to particles of lower energies. This phenomenon is not necessary tested by radiation tests, performed by applying particles of higher energy. By a sputterd TiOX adhesion layer underneath a protected Au-coating (protected by an Al2O3-Si3N4-laminate), resistance against interdiffusion, and the successful passing of radiation-, cleanability- and abrasion tests could be achieved. This high reflective coating (reflectivity of 98 % at 1064 nm) was applied to the different mirrors of the GALA-instrument.