Scanning strategy for surface defects evaluation of large fine optical components

Abstract

Defects, such as scratches and digs etc., play an important role in quality control of fine optical components. Dark field microscopic imaging has become one of the most commonly means for surface defects detection. However, the imaging field of view is very limited compared with the increasing aperture of the test parts and sub-aperture scanning is usually employed to increase the detection aperture while ensuring the system resolution. The problems that classic “S” Shape Sub-Aperture (SSSA) strategy faces are the high positioning accuracy requirement for the translation stage and the time-consuming processing of huge number of sub-apertures. Herein, a Sub-Region and Sub-Aperture (SRSA) scanning strategy is proposed. It divides the aperture of test part into sub-regions. Within each sub-region, classic scanning strategies and stitching methods can be employed the same time when next sub-region is being scanned. The whole aperture of the test part can be obtained when all the sub-regions are stitched together. Thus the positioning accuracy requirement of translation stage is reduced from the whole aperture to a sub-region while most of the sub-aperture stitching and processing time is covered within the scanning process. The relationship between the positioning accuracy of translation stage and the sizes of sub-aperture/sub-region is discussed in detail. Comparison experiments show the superiority of the proposed SRSA scanning strategy with which large-aperture, high precision scanning detection of large-aperture optical components can be accomplished efficiently and economically.