Abstract

Front surface metal mirrors made by vapor deposition of aluminum or silver onto glass substrates are widely used in optical systems. Because of their inherent mechanical and environmental weakness, they need to be protected with hard dense dielectric layers. While much research has been done in the past to optimize these protective coatings, conventionally protected aluminum and silver mirrors are still less than optimal in their environmental durability. This is due to the packing density of less than unity of the protective coatings, which allows water vapor and other adverse agents to penetrate the coatings and attack the metal film. Substantial improvements of protective layers have been reported for ion assisted deposition, which, however, may have remained in the laboratory scale. Low-voltage reactive ion plating deposition of oxides has been shown to produce very dense homogeneous films, which we applied as protective layers for aluminum and silver thin films. The technique is being used in a 32-in. standard high vacuum box coater, which makes it potentially useful for coating of large mirrors of up to 30-in in diameter.

© 1988 Optical Society of America