Abstract

A white-light source is used so that good interference occurs only when the two paths are equal, that is, when both primary mirror’s segments are the same distance away from the interferometer, e.g. with a double-image prism in the adaptive telescope. When observing a small step between surfaces with comparable reference dimensions, interference fringes are usually formed in white light that are perpendicular to the boundary line between the surfaces. An interferometer with white-light source is based on a prism design that includes a rectangular prism with a beamspliter hypotenuse face to which an additional prism is cemented to form a double-image compound pentaprism. It makes possible to monitor the step between the elements of a compound primary mirror more simply than in an interferometer with Kosters prism. This is because of the almost complete compensation of the optical path length in a system with counterpropagation of the interfering beams. Preliminary phasing of primary mirror segments during assembling process may be accomplished with help of a such ambiguity sensor. The experimental investigations with visual control showed a possibility to recognize displacement of 1/20 wavelength. This investigation was fulfilled at the special test bench with high resolution laser interferometer. The interferometer resolution is 1 nm.

© 1995 Optical Society of America