Wavefront sensor employing novel d.c. shearing interferometer

Abstract

A wavefront sensor employs a novel DC shearing interferometer which produces four interferograms which are 90.degree. phase shifted with respect to each other. The incoming wavefront is replicated into two beams, a portion of each being reflected off of a beamsplitter and the remaining portion being transmitted therethrough, at first and second portions of the beamsplitter. After leaving the beamsplitter the transmitted and reflected beams are reflected back 180.degree. by a pair of retroreflectors, and directed at third and fourth portions of the beamsplitter. The retroreflectors are adjusted to produce four shearing interferograms and a quarter wave plate is positioned in the path of one of the beams to cause the four interferograms to have a 90.degree. phase shifted relationship with respect to each other. The interferograms are thereafter projected upon intensified self scanning diode arrays, which digitize the interference patterns for convenient processing by means of a four-bin algorithm, which in turn generates estimated phase data indicative of the shape of the wavefront in a given direction. The process may be duplicated to produce second measurements in an orthogonal direction, which enables the mapping of the wavefront in both X and Y. In contrast with A.C. shearing interferometers, the wavefront shapes of very brief plused beams of light may be measured.