Development of a zero-method interferometer by means of dynamic generation of reference wave front

Abstract

In this report, we propose a zero-method interferometer by means of dynamic generation of reference wave front using liquid crystal type spatial light modulator (LCoS-SLM). This interferometer was developed to aim to measure the shape of complex plane, such as aspherical plane. It is difficult for interferometer to measure such a surface which include large inclination, because of the problem of saturation of interference fringe. To overcome this problem, and to enlarge the dynamic range of interferometer, we attempted to combine interferometer and zero-method. Zero-method is characterized by its wide dynamic range. To apply zero-method to interferometer, SLM is adopted to configure variable reference surface. The basic configuration of the developed interferometer is Twyman-Green interferometer. A SLM is placed instead of reference mirror. In this interferometer, the shape of a target is measured using interference between object wave front and reference wave front that is generated using SLM. At first, the SLM generates flat wave front. And the detected phase map is fed back to the SLM. Then the difference between object wave front and detected phase map in the first turn. The operation is recursively repeated until the phase range of detected phase map becomes under the threshold. Then the generated wave front should become equal to the target shape. In this report, the basic idea of zeromethod interferometer using LCoS-SLM is verified through several numbers of simulative experiments.