Stresses developed in optical film coatings.

The development of stress in evaporated dielectric and metal films, used as optical coatings, has been investigated experimentally by observing the bending of a thin silica strip as it becomes coated. The strip forms one mirror of a laser interferometer mounted within the coating chamber, giving high measurement sensitivity. Stress data on a number of materials commonly used in coating are presented, and the behavior of multilayer coatings investigated. Analysis of the effect of film stress upon the figure of optical surfaces is given, and the influence of stress upon the mechanical stability of multilayers is discussed.