System optimization of radial shearing interferometer for aspheric testing

Abstract

The large slope of the aspheric departure presents great difficulty for optical testing researchers to test aspheric surfaces and wavefronts. The instrument dynamic range of traditional interferometers does not support the high number of fringes due to the steep slopes commonly found in aspherics. The radial shearing interferometer, which can greatly reduce the slope of the aspheric wavefront under test, is always adopted to test aspherics. In this paper, the two evaluating parameters of a radial shearing interferometer, the wavefront slope tolerance and the wave phase sensitivity, are proposed. The effective radial shear plays important role in reduction of the wavefront slope and that of the wave phase sensitivity. How the two parameters effect the radial shearing interferometer is discussed in detail. Computer simulation shows that by properly choosing the effective radial shear, the radial shearing interferometer can obtain the best performance when testing an arbitrary aspheric wavefront. This research is of greatly importance to the design of the radial shearing interferometer for aspheric testing.