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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.

Local displacements in the plane of an object surface illuminated by coherent light may be measured by recording double-exposure photographs of it. When the surface is illuminated symmetrically by two oblique beams, 'speckle correlation fringes' appear in the doubly exposed negative, due to the nonlinear nature of the photographic recording. Factors affecting the visibility of these fringes and the range of displacement which can be measured are discussed. The fringe visibility falls to zero for displacements larger than a speckle width, but measurements can then be performed upon the optical transform of the negative image. With uni-directional object illumination, the in-plane displacement can be measured on a point-by-point basis in magnitude and in direction from Young's fringes observed. With two symmetrical oblique illuminating beams the effect of a small surface strain is displayed, even if large lateral displacement has occurred, by using spatial filtering when viewing the photographic image.

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