Highly Reflective Silver-Enhanced Coating with High Adhesion and Sulfurization Resistance for Telescopes
Hsing-Yu Wu, Shaorong Huang, Chih-Hsuan Shih, Li‐Jen Hsiao, Hongwei Chen, Ming-Chung Cheng, Jin–Cherng Hsu
Abstract
Highly reflective metal coatings are essential for manufacturing reflecting telescope mirrors to achieve the highest reflectivity with broad spectral bandwidth. Among metallic materials, enhanced silver-based coatings can provide higher reflectivity in the 400-500 nm spectral range to better performance from visible to near IR. Moreover, over-coating a dielectric protective layer on the mirror's front side attains additional hardness and oxidation stability. In this paper, we study a combination of thermal and electron beam evaporation as a technology to form protected enhanced high reflective Ag coatings. A newly designed multiplayer film can pass ASTM 5B adhesive performance testing and give sulfurization inhibition. The average specular reflectivity for the enhancement coating is about 98% in wavelengths across the spectral range from 400-1000 nm. This innovation has been demonstrated on a Newtonian type telescope, with storage in an ambiance humidity H = 60-85%, and temperature T = 10-35 °C, for more than six months without degradation in coating performance.