Axial peak extraction in the measurement of subsurface structures with annular illumination confocal microscopy

Three-dimensional dark-field confocal microscopy (DFCM) using annular illumination and complementary detection apertures is capable of detecting subsurface defects in ultra-precision optical components. In this study, a DFCM tuning algorithm for large apertures is proposed based on the sinc² tuning model. This algorithm provides a reliable and theoretically accurate method for extracting the axial position during the measurement of subsurface defects. The rationality and accuracy of this method are verified through simulations and experimental results.