Empirical strategy for detection and removal of misalignment aberrations in interferometry

Misalignments of the object under test relative to the instrument's coordin ate system play an important role in interferometrical form metrology. Degr ees of freedom, coordinate systems, object symmetries, calibration methods, mathematical models, and misalignment terms are. closely interrelated. F-s pecially in low-symmetry applications like the testing of aspheres, specifi c models have to be elaborated and implemented. An alternative, flexible an d universal way to carry out misalignment removal is to use an empirical st rategy: For every degree of freedom the affiliated misalignment term is mea sured through the use of phase shifting interferometry. The terms obtained curing these measurements are then used to fit a set of misalignment coeffi cients to the data of the actual measurement, The method is discussed in de tail and, as a proof of concept, is demonstrated experimentally by the exam ple of the testing of high aperture microspheres.