Measurement of slopes and profile of an optical lens by shearography

Abstract

In this paper, an optical technique based on speckle-shearing interferometry and a double refractive-index method is employed for the measurement of surface slopes and profile of an optical lens. The lens to be studied is mounted on one side of a glass tank filled with water and illuminated with a collimated coherent light source. The lens image is captured on a photographic film placed at the image plane of an image-shearing camera. A second exposure on the photographic film is made after the container is refilled with a liquid of different refractive index. The resulting photograph yields a fringe pattern which represents lines of constant derivatives of the surface profile. Test results conducted on a plano-concave lens compared favorably with theoretical predictions. Copyright © 1996 Elsevier Science Ltd.