Spatially-Phase-Shifted Coherent Gradient Sensor for Full-Field Measurement of Surface Slope and Curvature

In this study, a spatial phase stepping method for coherent gradient sensing is developed to automatically measure the reflective surface slopes, curvatures and shapes in dynamic problems. A beam-splitting system and a spatial phase stepping system are designed to obtain four interferograms with different phase shifting steps in one shot. The post processing can automatically generate accurate full-field plots of the slope field components using the four interferograms per frame and the four-step phase shifting algorithm. The surface curvatures and shapes can be calculated numerically using the slopes. To verify this method, a thermal shock experiment is conducted using a reflecting mirror with a dielectric film. The highest temperature achieved during thermal shock was 672 degrees C. The frame rate is 25 fps and the results of every frame are obtained automatically. Experiments demonstrate the applicability of the proposed spatial phase stepping method.