The off-axis alignment of an asphere by a Fizeau interferometer

The mechanical position alignment of aspherical surfaces becomes a difficult challenge when the aspherical departure of the surface is high. An optically obscured aspherical surface is even more difficult to be aligned due to the missing obscured paraxial spherical vertex surface area for implementation of the auto-collimating technique. This research paper aims to develop a method to align an obscured aspherical surface with respect to the mechanical axis of a precision rotational stage by analyzing the multiple off-axis interferograms measured from a phase shifting Fizeau interferometer. The alignment induced linearly varying coma is successfully shown in the simulation results. The method can predict the vector direction of mis-alignment errors by least square fitting. An iterative process is possible to be implemented to bring the misaligned aspherical surface back to aligned status.