Empirical strategy for detection and removal of misalignment aberrations in interferometry

Misalignments of the object under test relative to the instrument's coordinate system play an important role in interferometrical form metrology. Degrees of freedom, coordinate systems, object symmetries, calibration methods, mathematical models, and misalignment terms are. closely interrelated. F-specially in low-symmetry applications like the testing of aspheres, specific models have to be elaborated and implemented. An alternative, flexible and universal way to carry out misalignment removal is to use an empirical strategy: For every degree of freedom the affiliated misalignment term is measured through the use of phase shifting interferometry. The terms obtained curing these measurements are then used to fit a set of misalignment coefficients to the data of the actual measurement, The method is discussed in detail and, as a proof of concept, is demonstrated experimentally by the example of the testing of high aperture microspheres.