Highly Reflective Silver-Enhanced Coating with High Adhesion and Sulfurization Resistance for Telescopes

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.

Study on environmental durability of nanolaminate silver-based films under edge protection

“…We focus on protection layers, which includes the surface and edge corrosion resistance of protection layers. For promoting surface resistance of the protection layer surface, the high and low refractive index medium materials with excellent corrosion resistance are usually selected and designed as the general two-layers structure [8], which can also meet the high reflectivity requirements of specific wavebands. The silver mirror with this protection layers structure can be used for many years under dry environment, while the recoating of the mirror will be fabricated after several months under humid environment.…”

“…The total thickness of the protective layer remains unchanged, the unit layer in the two-layer structure is further designed as the nanolaminate structure [9,10], which can improve the corrosion resistance of the protection layer. Many physical vapor deposition technologies is used to fabricate the films [11,12], where electron beam evaporation deposition is widely used for large aperture mirrors [8,13] at room temperature. The packing density of the film can be improved through ion source assistance.…”

A solution-processed radiative cooling glass

“…However, organic polymers tend to yellow and degrade over time when exposed to ambient conditions ( 17 , 28 ), including ultraviolet (UV) light, heat, water, and ambient chemicals (e.g., NO x , SO x , and O 3 ), which increases the material’s solar absorption, thus reducing the cooling power or even resulting in heating. In addition, the metals used in polymeric or inorganic radiative cooling structures, such as silver ( 19 , 29 ) and aluminum ( 20 ), can be oxidized or sulfated by chemical species found in air (O, O − , Cl − , H 2 O 2 , and SO 2 ) ( 30 ), which causes a reduction in solar reflectance ( 31 , 32 ). Clearly, environmental stability remains a roadblock in the practical implementation of this otherwise promising technology.…”

Editorial for the Special Issue “Applications of Optical Thin Films”

“…On the other hand, there are also articles related to the macro level, such as Cu et al's [7] study, wherein a dielectric diffraction grating designed with an efficient multilayer to enhance the laser damage threshold was developed. In addition, silver-enhanced coatings with high adhesion and sulfidation resistance for telescopes with a broad spectral bandwidth from 450 nm to 1000 nm were developed by Wu et al [8]. These articles focus on studying optical films and coatings at the macroscopic scale.…”