Thin-film optical coating filter stability under different environmental conditions

Experiments are conducted to determine the degree of moisture effects in optical thin-film coatings, to determine how to specify moisture stability of these films, and to ensure that performance levels are met after these films are exposed to all anticipated environmental conditions. Three testing techniques, an air oven, a vacuum oven, and water immersion, are evaluated to determine which techniques best characterize the moisture stability of these films. The filters tested fall into three categories, based on their degree of stability: type I, which are inherently stable, type II, which are basically stable except under extreme conditions, and type III, which are unstable.