Near-null compensator and figure metrology apparatus for measuring aspheric surfaces by subaperture stitching and measuring method thereof

摘要

A variable near-null compensator for measuring aspheric surfaces by subaperture stitching includes a pair of counter-rotating CGH phase plates, each of the phase plates having a phase function including two terms Z5 and Z7 of Zernike polynomials. The phase plates are mounted on a pair of precision rotary center-through tables, wherein rotational axes of the pair of precision rotary center-through tables coincide with the optical axes of the phase plates. A figure metrology apparatus includes a wavefront interferometer, the test mirror mount, the near-null compensator and the mechanical adjustment components therefor. The optical axis of the near-null compensator coincides with the optical axis of the interferometer. A method for measuring aspheric surfaces by subaperture stitching includes the steps of mounting the test mirror, measuring the subapertures with the figure metrology apparatus, and finally processing the data by stitching.