Determination of aspheric vertex radius of curvature in non-null interferometry.

Traditional spherical radius of curvature interferometry is not valid for an aspheric vertex radius of curvature (VROC) due to the obstacle in identifying null positions (cat's eye or confocal position). Simultaneous optimization for multiconfiguration of an interferometer model is proposed to retrieve the actual aspheric VROC from its biased nominal value. This procedure works out the contradiction between VROC deviation and positioning error and even surface figure error, independent of absolute positioning by cat's eye or confocal position. In this method, the aspheric VROC and surface figure can be measured simultaneously, which facilitates the test process remarkably in practical optical shop testing. Furthermore, the parent VROC of a hollow aspheric (annular surface) also can be determined in this method. The performance of the proposed method is validated by experiments.