Defect detection of precision optics by bright-dark-field structured illumination microscopy

Defect has become the bottleneck that limits the further increase of energy output in high-power laser devices, accurate defect detection is important for defect evaluation and optical component quality control. The bright-field methods have the problem that the illumination background light affects the measurement sensitivity. The dark-field measurement methods can remove the illumination background light, and the defect detection sensitivity is higher. However, the surface shape information is also removed out, thus the defect depth information is missing. In addition, the axial resolution of defect detection under regular illumination is rather low due to the influence of out-of-focus light. In this paper, a defect detection method based on bright-dark-field structured illumination microscopy (BDSIM) is proposed. This method takes the advantage of the high axial resolution of structured illumination, reconstructs the surface shape by bright-field configuration, and detects the surface and subsurface defect by dark-field configuration. Experiments prove that our method can effectively measure the surface and subsurface defects with accurate depth information.