Patent ID: 6344898
Filing Date: 2002-02-05
Classification: G01B,G01J

Abstract:
An apparatus for measuring a profile of an aspherical test surface of a sample, comprising:(a) a point light source configured and situated relative to the sample so as to produce, from an input light, a measurement beam of light propagating as a prescribed spherical wavefront from a point on the point light source to the test surface so as to reflect from the test surface; (b) a beamsplitter situated so as to receive light of the measurement beam reflected from the test surface, the beamsplitter being configured to split the reflected measurement beam into first and second measurement-beam portions each propagating along a respective path; (c) a light-diffraction element situated in the path of the first measurement-beam portion, the light-diffraction element being configured to diffract the light of the first measurement-beam portion into multiple orders of diffracted light and situated so as to cause the diffracted light to interfere with light of the second measurement-beam portion and produce interference fringes; (d) a detector configured and situated so as to detect the interference fringes; and (e) an optical element situated between the test surface and the beamsplitter and configured so as to convert the aspherical wavefront of the measurement beam reflected from the test surface into a desired spherical wavefront.