Research on the DF-TSOM method for detecting subsurface defects of optical components

In response to the growing need for detecting subsurface defects at the hundred-nanometer scale, this study introduces what we believe to be a novel dark field through-focus scanning optical microscopy (DF-TSOM) technique. Subsurface defect samples were prepared with a depth of 100 µm and diameters of 1 µm, 0.4 µm, 0.2 µm, and 0.1 µm for experiments. Results demonstrate that DF-TSOM successfully detects subsurface defects with diameters 0.1 µm, a feat unattainable with traditional TSOM, which failed to accurately detect subsurface defects with diameters 0.4 µm. DF-TSOM improves the contrast by approximately 10 times compared to traditional TSOM when the subsurface defect diameter is 1 µm. This study presents a promising new approach for the detection of subsurface defects in transparent materials, offering advantages such as high sensitivity, enhanced contrast, a simplified hardware setup, and the potential for online detection.