Abstract

We have reported¹ the development of a new viewpoint in AR coating design using inhomogeneous index (Rugate) functions. We have carried this to the practical application of the design principles to films composed of only homogeneous layers using two materials. Here we refine these applications by the use of three and four different practical indices. We discuss the possibilities and we demonstrate the limitations of the currently available indices (particularly low indices). The "ideal" broad band AR would have a smooth index profile from the substrate to the medium. This can be approximated by the use of many thin homogeneous layers. The major limitation is the need for a last layer of lower index than currently available. This causes the residual reflectance in the AR band to be higher than desired and/or the band width to be significantly narrower. We show how far these limits can be pushed in practical coatings with current materials.

© 1990 Optical Society of America