Optical free-form surface cascade null interferometry device and measurement method

Abstract

The application discloses an optical free-form surface cascade zero-position interferometric measuring device and a measuring method. A standard plane wave is modulated by a feedback-controlled deformable mirror and a liquid crystal spatial light modulator, the wavefront modulation amount generated by each adjustable phase element is monitored and feedback-controlled, and a large-curvature reference wavefront is generated by superposition. Another standard plane wave is irradiated onto a large-curvature optical free-form surface, and a large-curvature wavefront generated by reflection of the free-form surface is used as an object light wavefront. Through feedback control of the multi-stage adjustable phase elements, the reference wavefront and the object light wavefront are matched to the maximum extent, and zero-position interferometric measurement is realized. The two wavefronts are interfered on the surface of a CCD detector, and a small amount of phase difference remaining after the object light wavefront and the reference wavefront are matched generates easily-demodulated sparse interference fringes. By comprehensively utilizing the sparse interference fringe information and the wavefront modulation amount information of the cascade adjustable phase elements, the surface shape information of the measured free-form surface can be inversely reconstructed.