Absolute test technology for rotation and translation interference based on lightweight calibration mirror

The optical interference absolute test technology can separate the surface figures of the reference plane as well as the tested optics, and it is an effective means to calibrate the accuracy of the interferometer. For the calibration requirements of large-aperture plane interferometer, the rotation translation method only requires one transmission flat and one reflective flat, which avoids the cost and difficulty of processing an additional flat. However, with the increase of the caliber, the weight and support make the deformation of the reflective flat larger in various states of translation and rotation, and then affect the absolute test accuracy. Therefore, it was proposed to design a lightweight calibration mirror as a reflective flat, and used the rotation translation method to realize the absolute test of the large-aperture interferometer. The Φ 1 500 mm plane interferometer was used as the test requirement, the SiC was used as the calibration mirror material, and the lightweight design was carried out with a triangular lightweight structure and a six-point back support method. The weight was controlled to only 93 kg, and the surface deformation PV value introduced by the support and gravity was 9.75 nm. It superimposed this deformed surface shape to PV value of λ/4, and performed rotation translation absolute test simulation calculation for processing surface shapes of different distributions. For the surface shapes with low degree of rotational symmetry and containing more high-frequency components, the test accuracy is λ/30, and for the smooth and symmetrical surface shapes, the test accuracy can reach to λ/50. Therefore, in order to achieve the λ/50 accuracy calibration target for the large-aperture plane interferometer, it requires that the PV value of the processed surface of the SiC calibration mirror is lower than λ/4, try to avoid high-frequency components, and have a high degree of rotational symmetry.