Measuring the radius of curvature of a spherical surface with diffraction method

Abstract

A new diffraction method for measuring the radius of curvature of a convex spherical surface with a large radius is proposed. It is based on measuring the diffraction intensity profiles produced by a designed slit. This diffraction slit is built up using two straight edges. The upper straight edge remains fixed and the lower one is located on the spherical surface, so that the slit width can be modified with moving the lower straight edge on the spherical surface of a sample. The diffraction patterns are captured by a line CCD, and the extremum positions can be ascertained accurately through applying least-square fitting for the intensity distribution curves. By establishing the relation between the displacements of the lower edge in two mutual perpendicular directions and the radius of curvature of the sample, the radius of curvature of the test spherical surface is obtained. Experimental demonstration of the diffraction method on a spherical surface is performed.