Abstract

Multilayer coatings have a propensity for the absorption of moisture depending on the porosity and/or density of the materials making up the thin film structure¹. To some extent the degree of absorption can determine the durability of the coating and definitely affects the optical performance as the absorbed water molecules fill voids in the materials causing an increase in film indices. This effect can show up as a molted or blotchy appearing coating if the absorption is non-uniform, or irregular, over the surface of the coating or it can be a uniform shifting of the edge for multilayer edge filters². For applications requiring tight transitions between transmission and reflection (beamsplitters) or high OD rejection of narrow visible bands with high photopic throughput (laser eye protection filters) this phenomenon translates to reduced manufacturing tolerance. Experiments were conducted in order to understand the degree of this effect and to determine how to specify moisture stability testing to assure meeting performance levels upon exposure to all anticipated environmental conditions.

© 1992 Optical Society of America