Radius of curvature measurement by Twyman- Green's interferometer

The radius of curvature of a spherical surface has been measured by a non-contact interferometric method using Twyman-Green's interferometer. This interferometer has been used without adding the traditional moving focusing lens in one of its arms. Similar to Newton's rings method, a single interferogram gives the radius of curvature of the spherical surface. Six spherical mirrors, both convex and concave, with radii ranging from 959 mm to 2221 mm have been measured. The results of the measurements have been compared with those obtained by Newton's rings method.