Quadriwave Lateral Shearing Interferometer Based on a Crystal Orthogonal Shear Displacer

To effectively solve the transmissivity limitation problems of two-dimensional gratings used for the QWLSI in aspherical surface measurement, and the non-uniformity of diffraction light intensity. A novel and simple quadriwave lateral shearing interferometer (QWLSI) for aspherical surface based on a crystal orthogonal shear displacer (OSD) is proposed. The OSD system is formed by adopting two-crystal polarization parallel beam displacers (PBDs), which can make it achieve the orthogonal shearing in the x- and y-directions simultaneously. The lateral shearing interference waves of four-beam overlapped replicas are simply generated in OSD orthogonal directions without any bulky and complicated optical components. when the overlapped replicas incident to the polarization angle of the analyzer set as 45° or 135°, the synchronous QWLSI interferogram information can be obtained in real-time. This QWLSI interferogram itself carries less noise, and a high-precision phase profile can be obtained by simple spectrum denoising. In this study, the proposed method was theoretically described and verified by measuring aspheric samples discussed with comparison to the measurement results with a well-established interferometer. This interferometry has made it possible to improve the stability and feasibility of aspherical surface testing experiments.