Dark-field structured illumination microscopy for highly sensitive detection of 3D defects in optical materials

Precise three-dimensional (3D) inspection of surface and subsurface defects for optical components has become more and more urgent in high-power laser systems. In this paper, a dark-field structured illumination microscopy (DSIM) is proposed for 3D defect detection method in optical components. This method improves the axial reso-lution by structured light modulation, and enhances the defect imaging sensitivity by a high-pass spectrum filter placed at the spectrum plane of the microscopic system. Experiments prove that our method performs well on de-tecting sensitivity and axial resolution. It can measure the 3D defects of both flat and curved optical components, and the detection depth range is wide enough to cover the subsurface defect depth of polished optics. Therefore, the DSIM provides the possibility for a more accurate and complete evaluation of optical components' quality.