Simple wedge plate based lateral shearing interferometry technique for coherent alignment of tiled grating assembly

Abstract

A simple, sensitive and robust technique is proposed for coherent alignment of tiled grating assembly using wedge plate lateral shearing interferometry. In this technique, two thick glass wedge plates are used to generate interferograms from reflected and diffracted laser beams, from the tiled grating assembly under alignment. This single optical element based interferometric technique is easy to set up, insensitive to the vibrations and provides simultaneous information of both reference as well as error interference patterns, which are used to estimate the alignment errors. Performance of this technique was tested through alignment of two reflective gratings (size 140 mm X 120 mm), with an angular and translation sensitivities of less than 1 μrad and 50 nm respectively.