Determining parent radius and conic of an off-axis segment interferometrically with a spherical reference wave

Abstract

A simple interferometric method is presented for determining the parent radius of curvature (ROC) and conic constant (CC) of a conic surface. This method compares the test surface with a spherical reference wavefront having a ROC equal to the local sagittal, medial, or tangential ROC. The measured wavefront aberrations, particularly the astigmatism and coma, and local radii are used to determine the parent ROC and CC. This method does not require null optics or knowledge of the surface coordinate where the measurement is made.