Laser reflection differential confocal large-radius measurement for concave surfaces

In this paper, a laser reflection differential confocal large-radius measurement (RDCLM) method is proposed for concave surfaces. Based on the property that the zero point of the axial intensity curve precisely corresponds to its focus in a laser differential confocal system, RDCLM precisely identifies the positions of the surface vertex of the test lens and the last surface vertex of the objective lens, and obtains the moving distance L of the test lens. Finally, RDCLM obtains an accurate radius of curvature (ROC) of the test lens using L, the focal length f of the objective lens, and the system aperture D. Preliminary theoretical analysis and experimental results show that the RDCLM relative measurement uncertainty is 0.003% for a concave lens with a ROC of −5003 mm.