Reflectivity enhancement of silver-based mirror in the wavelength range 400nm-450nm

Abstract

With the development of remote sensing technology, the short working wavelength has been extended to 400nm in many current international spatial optical remote sensors. However, the reflectance in the wavelength range from 400nm to 450nm cannot meet the requirement for silver-based mirror. In order to solve this issue, SiO2 and Ta2O5 used as reflectivity enhancement layers are deposited on the silver layer. Simultaneously, the two dielectric films also protect the metallic silver film to from corroding in complicated environment. During the deposition process of Ta2O5 dielectric coating material, oxygen partial pressure, anode voltage and current of the ion source are optimized to get higher refractive index. The values of stress of the SiO2 layer and theTa2O5 layer are analyzed to get the adhesive coatings by the Stony formula and the process parameters of SiO2 dielectric coating material are obtained. The optical constants of these two dielectric films are established by using the Cauchy dispersion formula and the incoherent reflective theory, and then the thicknesses of them are optimized by simplex algorithm. SiO2 layer and Ta2O5 layer are sequentially deposited on the silver layer. The measurement results show that the average reflectivity of the wavelength ranges 400nm-450nm and 400nm-900nm reaches over 95% and 98%, respectively. The reflectivity enhanced silver-based mirror also passes the adhesion test according to relevant technique requirements.