Common-path interferometry with tilt carrier for surface measurement of complex optics.

We propose a novel common-path non-null interference system for the surface measurement of complex optics. Because of the common-path structure, systematic errors are mostly eliminated and the complexity of system calibration is reduced for the proposed setup. However, optical design of common-path non-null interference systems is of great difficulty because many off-axis beams are used to compensate for the local gradient of the measured piece. Different from the classical common-path interferometers, which pay more attention to the beam quality of the on-axis field of view (FOV), the proposed system requires better quality for both on-axis and off-axis outgoing beams. In the proposed setup, the lens groups with wide FOVs afford wave aberrations better than 0.1λ for the on-axis and off-axis FOVs. Simultaneously, the off-axis beams are prevented from generating pseudo reference beams by optimizing the parameters of the lenses and the aperture. In addition, multiple tilted test beams are generated by a point-source generator based on a fiber array, which is more versatile than a lens-array-type point-source generator. Further, a universal measurement system with high accuracy and time savings is formed, as evidenced by the measurement results of a parabolic mirror and different types of cylindrical mirrors.