Polarization grating based circular subaperture stitching interferometer insensitive to vibration and alignment error.

The subaperture stitching interferometry can extend the dynamic range of the interferometer and is widely used for high-resolution measurement of large-aperture, high-slope aspheres. Most subaperture stitching interferometry requires a high-precision multi-axis motion control system and a vibration-free environment. This paper proposes a polarization grating-based circular subaperture stitching interferometer assisted by a virtual-real combination algorithm to realize non-null measurement insensitive to vibration and alignment error. A polarization grating that scans subapertures through its axial rotation is adopted in place of the multi-axis motion control system. Polarization phase-shifting interferometry is introduced to achieve transient measurement of a single subaperture. Compared with traditional subaperture stitching interferometers, the proposed system is more compact and reduces measurement errors introduced by mechanical adjustments, improving the insensitivity to the vibration of individual subaperture measurements. Additionally, a virtual-real combination algorithm effectively suppresses retrace errors, reduces the impact of alignment errors on measurement accuracy, improves the overall insensitivity to vibration of subaperture stitching, and avoids positioning and calculation errors caused by complex stitching algorithms. The feasibility of the system and method, as well as their merits in insensitivity to vibration and large alignment tolerance, are verified through experiments. This research provides innovative and instructive insights into the application of polarization grating-based circular subaperture stitching interferometers.