We investigate three-flat calibration methods for circular flats, based on rotation symmetry and mirror symmetry, for absolute interferometric flatness measurements in the presence of deformations caused by the support mechanism for the flats, which are a significant problem for large, heavy flats. We present a novel solution to the three-flat problem for flats with mounting-induced deformations. In the new three-flat solution, the flat deformation is calculated along with the wavefront flatness errors for the three flats. Formulas for the uncertainty of three-flat solutions are derived.
Citation: Optical Engineering
Pub Type: Journals
absolute flatness measurement, Interferometry, mounting-induced deformations, three-flat test, uncertainty