Long-Focal-Length Aspheric Wavefront Measurement Free-from Phase-Shifting by Reflective CGH and Physics U-Net

Measuring long-focal-length aspheric surfaces are susceptible to the environmental disturbances, where need long testing optical path. Thus, folding the testing path and no phase-shifting methods would be appreciated. Conventional transmissive computational generated holography (CGH) could not provide a folding test path. Meanwhile, conventional temporal phase-shifting methods could also be heavily influenced by the long path. To face this challenge, in this paper, a wavefront measurement method is proposed, free-from phase-shifting by a novel reflective CGH and physics U-Net. Here, the reflective CGH solution is for aspheric null measurements, folding the testing path. A comparative analysis was conducted between reflective and transmissive CGHs under laboratory conditions. A root-mean-square (RMS) difference of 0.002λ was observed. Principal component consistency (PCC) was achieved at 0.9905. Notably, the working distance of the former configuration was found to approximate half that of the latter. Wavefront phase retrieval uses the physics-informed U-Net deep learning method. An average accuracy of 0.007λ is achieved by the phase retrieval results derived from two carrier interferograms using the proposed method. This advancement effectively mitigates environmental disturbances associated with extended working-distance measurements, providing a novel method for long-focal-length aspheric wavefront measurement in astronomical telescopes and related fields.