<title>Measurement of steep aspheres: a step forward to nanometer accuracy</title>

Abstract

It is a promising method for measuring steep aspheres and complex surfaces with nanometer and sub-nanometer accuracy to measure the curvature and to calculate the topography from it, since unlike slope and distance, the curvature is an intrinsic property of a surface and less insensitive to error influences. For the development of a measuring instrument based on the physical property of curvature, various topics have been investigated. The method described does not rely on external form references, and the errors of the scanning stages and the whole-body movement of the artifact have only little influence on the accuracy. In comparison to other measuring techniques, it is an advantageous feature of the curvature measuring technique that distance and angle between sensor and surface element can be controlled and kept constant during scanning as it is the curvature and not the distance or the slope which is the measurand. This leads to the result that, apart from the calibration of the curvature sensor, the whole system no longer suffers from first-and second-order errors. The uncertainty budget shows that nanometer accuracy is achievable.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.