Research on measurement of in-plane displacement by objective speckle under spherical wave illumination

Objective laser speckle has been widely applied to optical imaging, surface roughness, micro-displacement, deformation measurement, etc., and spherical wave illumination is an important factor limiting its application. In this experiment, an optical system of in-plane displacement based on objective speckle has been set up, and the in-plane displacements under different spherical wave illumination are measured by the digital image correlation method. Then, the influence of the spherical wave on the measurement error is theoretically discussed, showing that under spherical wave illumination, the in-plane displacement should be corrected by a system magnification to reduce the measurement error. In addition, the measurement limits of different spherical waves are also compared and analyzed. This result can provide a certain reference for practical applications.