Patent ID: 8314937
Filing Date: 2012-11-20
Classification: G01B

Abstract:
1. A measurement method of illuminating a surface to be tested having an aspheric surface using light beams that form spherical waves, and measuring a figure of the surface to be tested, the method comprising: a first detection step of positioning the surface to be tested at multiple positions by moving the surface to be tested along a direction of an aspheric surface axis of the aspheric surface, with a center of curvature of the spherical waves aligned with the aspheric surface axis, and detecting interference patterns between light beams from the surface to be tested and light beams from a reference surface at each of the multiple positions; a second detection step of positioning the surface to be tested at multiple shift positions, at which the surface to be tested has been shifted from the multiple positions respectively by a known amount in a direction perpendicular to the aspheric surface axis, and detecting interference patterns between light beams from the surface to be tested and light beams from the reference surface at each of the multiple shift positions; a first calculation step of calculating an optical path length difference between a first length, which is between the center of curvature of the spherical waves and a paraxial center of the surface to be tested, and a second length, which is between the center of curvature of the spherical waves and a measurement position on the surface to be tested at which the light beams that have passed through the center of curvature of the spherical waves are perpendicularly incident, based on the interference patterns detected in the first detection step and the second detection step for each of the multiple positions and each of the multiple shift positions; and a second calculation step of determining the measurement position for each of the multiple positions based on the optical path length differences calculated in the first calculation step for the multiple positions and the multiple shift positions, and calculating a figure error, which is a difference between the optical path length difference obtained from a design value of the surface to be tested at the determined measurement position, and the optical path length difference calculated in the first calculation step for each of the multiple positions.