Due to the lack of rotational symmetry, off-axis two-mirror freeform optical systems usually exhibit coupled alignment degrees of freedom and poor sensitivity-matrix conditioning, which increase the difficulty of alignment. To address this issue, a geometrically constrained alignment method based on a multi-zone computer-generated hologram (CGH) is proposed. A multi-zone CGH integrating null compensation and mark projection on a single substrate was designed to provide both wavefront and spatial references. In combination with a staged alignment procedure, the projected optical marks were used to assist in establishing the relative positional relationship between the interferometer–CGH subsystem and the PM-SM system, while also providing geometric references for secondary-mirror pose adjustment during wavefront-guided iterative alignment. Results from multiple alignment experiments show that the mean wavefront RMS was 0.0577λ at 632.8 nm, with a standard deviation of 0.004λ. These results suggest that, under the present experimental conditions, the proposed method exhibits good repeatability and convergence stability and can provide a reference for the alignment of freeform optical payloads.
Wang et al. (2026) studied this question.