Triple-Layer Antireflection Coatings on Glass for the Visible and Near Infrared

Abstract

Triple-layer antireflection coatings on glass (n≈1.5) can provide a broader region of low reflectance than single- or double-layer coatings. Of the possible triple-layer combinations, the quarter-half-quarter construction has been found to be most suitable for the visible and near infrared. Calculations of reflectance as a function of wavelength have been carried out for many combinations of indices and for thickness variations. The effectiveness of the coatings is not much affected by small thickness variations of the two inner layers but does depend quite strongly on the thickness of the outer layer. Reflectance curves for various angles of incidence have been calculated for coatings matched both at normal incidence and at various given angles of incidence. Durable coatings have been prepared which have a single-surface reflectance of less than 1% from 415 to 840 mμ, with a corresponding range for the near infrared. The materials which have been used in the preparation of these coatings are: outside layer, MgF2; middle layer, SiO, ZrO2, ZnS, CeO2, and Nd2O3; inside layer, CeF3 and SiO.