Measurement of surface shape and deformation of small-aperture mirrors based on Coaxial normal incidence speckle deflectometry system

For small-aperture aspheric mirror surface measurement, the traditional measurement method phase measuring deflectometry (PMD) requires multi-step phase shifting, and the result is not high in accuracy and complicated in operation. The digital image correlation (DIC) that can be used for transient measurement is mostly used for diffuse reflection. surface. At present, a speckle deflection technique combining the former two methods has appeared, but its optical system is based on the traditional triangulation method, which has problems of angle occlusion and defects. This paper improves the speckle deflection algorithm and optical path system, replacing the traditional triangulation optical path system with Coaxial normal incidence speckle deflectometry system (CNISDS), adding a plate beam-splitter and a telecentric camera.On the one hand, it can avoid the changes in the shape of the captured image caused by perspective, and on the other hand, it can effectively avoid angle occlusion and missing information. Among them, the DIC method is used for image matching, the PMD method is used to calculate the displacement distribution. Then use the slope data to calculate to reconstruct the surface shape. The improved method can measure absolute surface shape and deformation at the same time, and has the advantages of simple measurement steps, fast response speed, and low cost. Finally, the correctness and feasibility are verified by simulation and actual measurement with deformable mirror. Compared with the phase-shifting operation which has complex steps or the low-precision mirror profile measurement results, the improved method is effective and superior, and provides a new idea for measuring small-aperture aspheric mirrors.