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Proceedings Paper • Open Access

Protected silver coatings for reflectors

Paper Abstract

For ground- and spaced based applications, Ag coated reflectors are indispensable because of their high reflectivity. The transport, assembling and storage of these reflectors takes a long time, before they are finally commissioned for the actual applications. To endure this period without a decrease of reflectivity, protective coatings with a final layer, which offers a high resistance to aqueous solutions and a low mechanical stress should be used. These criteria were taken into account for the selection of a final layer for a protected Ag-coating, which was applied for reflectors utilized in the CRIRES+- instrument (an IR spectrograph used at the VLT). Reactively sputtered Al2O3, SiO2 and Si3N4 layers were investigated with regard to these criteria. In aqueous (basic) solutions, the investigated Si3N4 layers are more stable than the SiO2 layers, and the SiO2 layers are more stable than the Al2O3 layers. This shows the influence of the intrinsic material properties. The mechanical stress of the sputtered layers depends on the deposition conditions and thus on the selected parameters. A Si3N4 layer with a high resistance to aqueous solutions also offers a low and stable mechanical stress. Therefore, the deposition-parameters which have been used for this layer were applied for sputtering the final layer of the protected Ag-coating for the reflectors.

Paper Details

Date Published: 12 July 2019
PDF: 10 pages
Proc. SPIE 11180, International Conference on Space Optics — ICSO 2018, 111804M (12 July 2019); doi: 10.1117/12.2536085
Show Author Affiliations
Stefan Schwinde, Fraunhofer Institute for Applied Optics and Precision Engineering (Germany)
Mark Schürmann, Fraunhofer Institute for Applied Optics and Precision Engineering (Germany)
Ralph Schlegel, Fraunhofer Institute for Applied Optics and Precision Engineering (Germany)
Jan Kinast, Fraunhofer Institute for Applied Optics and Precision Engineering (Germany)
Reinhold J. Dorn, European Southern Observatory (Germany)
Jean Louis Lizon, European Southern Observatory (Germany)
Sebastien Tordo, European Southern Observatory (Germany)
Norbert Kaiser, Fraunhofer Institute for Applied Optics and Precision Engineering (Germany)


Published in SPIE Proceedings Vol. 11180:
International Conference on Space Optics — ICSO 2018
Zoran Sodnik; Nikos Karafolas; Bruno Cugny, Editor(s)

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