Refining optical testing accuracy through advanced on-axis deflectometry

Phase Measuring Deflectometry (PMD) is a cost-effective, non-contact method for inspecting specular surfaces with interferometer-level accuracy. However, conventional off-axis layouts introduce wavefront error from the tilt and skew ray propagation through the system, which affects measurement precision. Additionally, uncertainty in Unit Under Test (UUT) positioning leads to errors in low-order surface shape measurements. This paper proposes an on-axis deflectometry setup with a laser distance sensor to improve accuracy. Through experiments and simulations, we assess systemic surface reconstruction errors caused by UUT positioning uncertainty, particularly in defocus, astigmatism, and coma. By analyzing and calibrating positioning errors, we enhance the accuracy and reliability of deflectometry for optical testing.