Patent ID: 7218403

Claim:
An interferometric scanning method for measuring rotationally and non-rotationally symmetric test optics having aspherical surfaces, said method comprising the steps of: generating at least a partial spherical wavefront along a scanning axis through the use of a decollimator carrying a spherical reference surface positioned along said scanning axis at a known location; aligning a test optic with respect to said scanning axis and selectively moving said test optic along said scanning axis relative to said spherical reference surface so that said spherical wavefront intersects the test optic at the apex of the aspherical surface and at one or more annular zones where the spherical wavefront and the aspheric surface intersect where their tangents are common; imaging the test surface onto a space resolving detector to form interferograms containing phase information about the differences in optical path length between the spherical reference surface and the test surface; interferometrically measuring the axial distance, ν, by which said test optic moves relative to said spherical reference surface; and analyzing said interferograms to determine the deviation in shape of said aspheric surface compared with its design in a direction normal to the aspheric surface based on the axial distance, ν, and the phase information contained in said interferograms and providing output data of said deviation.