Proposed extension of double-ended gauge block interferometers for measuring spheres

Double-ended gauge block interferometers (DEI) are becoming more and more established. This paper suggests its extension for enabling interferometric measurement of diameter topographies of spheres as an alternative to the existing spherical Fizeau interferometers. The extension essentially consists in the addition of two lenses which are as similar as possible, which are arranged symmetrically around the sphere to be measured. The determination of the diameter topography from the interferometric measurements with inserted and without sphere in the extended DEI is derived and specific aspects are discussed. An adjustment strategy for the extended DEI is also suggested. In conclusion, the proposed extension appears to be a promising measurement tool, especially for measuring small spheres, as required for applications in coordinate metrology.