A laser reflection differential confocal large-radius measurement (RDCLRM) method is proposed to meet the requirements of high-precision measurement for a large radius of curvature (ROC). The RDCLRM identifies the converging point of the multiply reflected test beam by using the differential confocal focusing technology. It then measures the distance between the positions of the test lens corresponding to these converging points for different reflection times. Therefore, a precise and high-efficiency measurement of a large ROC is achieved with a shorter measurement lightpath. The theoretical analyses and preliminary experimental results indicate that RDCLRM has a relative expanded uncertainty of better than 0.005% (k = 2). (C) 2015 Optical Society of America
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