Physikalisch-Technische Bundesanstalt

Science and industry's need for measuring the flatness of increasingly larger optical surfaces is constantly growing. Test pieces with a diameter of 600 mm are no longer rare. Such large surfaces can now be measured with interferometers which are smaller than the surface itself. With the new rotation stitching, as many partial topographies as desired are taken, while the test piece to be measured is rotated. Through the special arrangement of the test piece, gravity's disturbing influences can moreover be eliminated, as measuring near the points of support can be avoided. The procedure is, thus, not only considerably cheaper than previous measuring methods, but also more accurate in such an application. Measurement uncertainties in the nanometer range are achievable.