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Critical processing temperature for high-performance protected silver mirrors

Critical processing temperature for high-performance protected silver mirrors Abstract.Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin-film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving the overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60°C to 300°C, and then the mirror samples underwent an environmental stress test at 80°C and 80% humidity for 10 days. While all the mirror samples annealed below 200°C showed negligible corrosion after undergoing the stress testing, those annealed below 160°C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200°C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Astronomical Telescopes, Instruments, and Systems SPIE

Critical processing temperature for high-performance protected silver mirrors

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References (43)

Publisher
SPIE
Copyright
© 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)
ISSN
2329-4124
eISSN
2329-4221
DOI
10.1117/1.jatis.7.3.034002
Publisher site
See Article on Publisher Site

Abstract

Abstract.Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin-film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving the overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60°C to 300°C, and then the mirror samples underwent an environmental stress test at 80°C and 80% humidity for 10 days. While all the mirror samples annealed below 200°C showed negligible corrosion after undergoing the stress testing, those annealed below 160°C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200°C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation.

Journal

Journal of Astronomical Telescopes, Instruments, and SystemsSPIE

Published: Jul 1, 2021

Keywords: telescope; silver; mirror; protection; corrosion; deposition; annealing; reflectivity; film

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