High precision 3D optical detection technology based on shear interferometry with arbitrarily shear amounts

Differential interferometry is an effective method that has high contrast and can effectively overcome the "duplicate image" problem caused by shear interferometry. However, differential interferometry is limited by the addition of additional optical elements, such as grating, Nomarski, or Wollaston prisms, to realize shear interference, and the shear amount is difficult to adjust. A 3D shape reconstruction algorithm based on shear interference is proposed in this paper, which is appropriate for arbitrary shear amounts and directions. This algorithm overcomes the problem of duplicate images through an iterative phase addition approach, and simulated 3D morphology results of surface irregular defects are successfully reconstructed under arbitrary shear directions and shear amounts such that the maximum reconstruction error is only 10^-11 m. Furthermore, the morphologies of defects with large gradients can be obtained by adjusting the shear amount and applying an image interpolation approach, which can overcome the problem of phase ambiguity in monochromatic interferometry. Based on this algorithm, an optical testing system is designed that uses a mirror to adjust the shear amount and direction without adding additional optical elements to effectively simplify the experimental device and reduce the cost. Experiments are completed to confirm the feasibility of the proposed method, which can successfully obtain 3D morphology data of optical defects.