Progress on defect inspection for large-aperture optics

Progress report is made on the development of a multimodal inspection technique for surface/sub-surface defect characterizations of large-aperture optics. A high-speed laser scattering imaging with a sensitivity at 200-nm scale is used for defect discovery of large-aperture optics. The defect discovery provides statistical results of defects of the optics. After that, a multifunctional microscopic method is used for local defect review. A photothermal scanning microscopy is used for specific characterization of absorption defects, and a confocal microscopy is used for characterization of sub-surface defects. The defect review provides information for defect classification. Based on this multimodal technique, an inspection system is also developed and used for defect characterizations of large optics. Data analysis of the output of the system offers insight into the quality control process. In addition, a absorption distribution curve method is also proposed, which provides a new vision for evaluating the quality of large-aperture optics.