An investigation of the durability of front surface Ag mirrors using oxide protecting layers

Abstract

This paper describes the calculation of the reflection of front surface Ag mirrors and the investigation of the adhesion and durability of these mirrors deposited on the BK-7 glass surface. Cr, Al 2O 3, SiO x and Y 2O 3 underlayers and Y 2O 3, Al 2O 3, SiO x protecting layers were investigated. Layers were deposited by thermal evaporation and e-beam gun methods. Calculated and measured spectral characteristics are presented. All mirrors were subjected to the climo-mechanical tests and the results of durability of mirrors are presented. The following layer combinations BK-7/Cr/Ag/Al 2O 3 and BK-7/Al 2O 3/Ag/Al 2O 3/SiO x gave the best climo-mechanical characteristics and reflection of R > 96%for γ = 450–1100nm. Some layer combinations like BK-7/Al 2O 3/Ag/Al 2O 3 gave better spectral characteristics but durability was not satisfactory for practical application.