Patent ID: 7948638
Filing Date: 2011-05-24
Classification: G01B,G01M

Abstract:
1. An interferometric scanning method for measuring test optics having aspheric surfaces including those with large departures from spherical, said method comprising the steps of: generating a first wavefront from a known origin along a scanning axis; aligning a test optic on the scanning axis and selectively moving it along said scanning axis relative to said known origin so that said first wavefront intersects the test optic at the apex of the aspheric surface and at one or more radial positions where the first wavefront and the aspheric surface intersect at points of common tangency in circular zones around said scanning axis; interfering the first wavefront with a second wavefront to generate interferograms containing phase information about the differences in optical path length between the center of the test optic and the one or more radial positions; directing the interferograms onto a detector to provide an electronic signal carrying the phase information; measuring the axial distance, ν, by which the test optic is moved with respect to said origin; determining the detector pixel height corresponding to where the first wavefront and test surface slopes match for each scan position; determining the angles, α, of the actual normal to the surface of points at each zone as a function of the distance along the scanning axis; and using the angles, α, for determining information corresponding to the coordinates axial distance z and radial distance h of the aspheric surface at the common points of tangency.