Minimizing the Abbe-offset in interferometric radius metrology

摘要

For accurate radius of curvature measurements of spherical specimens on an interferometric radius bench, the axial displacement between the cat's eye position and the confocal position needs to be measured at the height of the optical axis of the form measuring interferometer. We propose an alignment technique which allows for the alignment of the Abbe-offset well below 100 μm within a few seconds based on fringe nulling. The alignment technique bases on a special designed optical element and a pre-adjustment procedure. The implementation of the alignment technique in a radius measurement setup with a repeatability of 30 nm will be shown.