Optical test using wedge plate phase-shifting lateral-shearing interferometer

Abstract

In order to test aspheric optical elements, wedge plate lateral shearing interferometer is used. In a wedge plate the thickness varies along the wedge direction. Because of this thickness varying characteristic, the optical path difference between the original wavefront and the sheared wavefront in wedge plate lateral shearing interferometer is changed according to the incident position of the ray. Simply moving the wedge plate in-parallel to the wedge direction gives the phase shift quantity required for phase shifting interferometry. In typical phase shifting methods, piezoelectric transducer(PZT) is mainly used to give phase shifting quantity. But this method requires only one additional linear translator to move the wedge plate. The required moving distance for the phase shift of wavefront in this method is an order of millimeter, whereas the typical moving distance in the other method using a piezoelectric transducer is an order of wavelength. This method has an advantage in the moving distance precision compared with the other methods. Using this wedge plate lateral shearing interferometer, optical wavefront is measured and reconstructed.