Absolute testing of flatness standards at square-grid points

Abstract

For the absolute interferometric testing of three unknown plane surfaces A, B, C, the surfaces can be combined in pairs in different positions. For such positional combinations a new rotation shift method is described. In addition to the three basic positions AB, BC, CA, this method uses one or two further positions that are reached by a 90° rotation and a parallel shift of one surface from the respective basic position. This makes it possible to determine the absolute flatness deviations of the three surfaces at the modes Q ij of a square grid whose grid spacing is equal to the shifting distance. In comparison with known methods, this has the advantage that, if image detectors of a square grid structure are used, it does not require any interpolations between the detector elements and the points Q ij. The basic equations and a method for their error-adjusted solution are stated. The solution is shown to be unique.