Optical coatings for large area interference filters

Abstract

The appearance of optical filters on large scale as heat reflecting coatings on domestic windows, heralds the advent of techniques and materials for a range of applications which are far removed from the ultra-high performance, and cost, of multilayer filters used hitherto. These new coatings use interference anti-reflection layers on either side of a thin metal layer. They are prepared by high rate reactive planar magnetron sputtering onto a large area of glass or plastic substrate. This technique is critically assessed and materials considered which will allow more complex filters to be made. In particular the preparation of a high index dielectric film of SnO 2 and a low index film of aluminium oxyflouride is described. Illustrations of some applications of these are given.