Zhenchuan Hu

To address the challenges of insufficient accuracy and poor versatility faced by conventional interferometers in measuring high-order aspheric surfaces, this paper proposes an optimized annular sub-aperture stitching method based on a reverse global planning strategy. The method initiates sub-aperture division from the edge region with the highest asphericity, aiming to maximize the effective measurement range of each individual sub-aperture and setting the minimization of the number of sub-apertures (N) as the core optimization objective. The algorithm features a concise structure, high stability, and ease of automation, enabling a significant extension of the interferometer's dynamic measurement range. Simulation studies demonstrate that the method effectively reduces the required number of sub-apertures, thereby suppressing the propagation and accumulation of mechanical positioning errors during the stitching process. Furthermore, by integrating this method with pinhole point diffraction interferometry (PPDI), a measurement system combining high accuracy and large measurement range is constructed. Experimental measurements of a convex high-order aspheric surface yield stitched results that are in excellent agreement with full-aperture measurements, with the peak-to-valley (PV) deviation of only 2.66 nm and the root-mean-square (RMS) deviation of only 0.44 nm. A detailed uncertainty analysis of the system confirms the reliability and reproducibility of the measurement results. This study not only provides an efficient method for the precision measurement of aspheric surfaces with large deviations but also offers a new technical pathway for enhancing the measurement capability and automation level of interferometers.

Precision measurement of aspherical mirrors is critical for high-end optical systems, where surface accuracy directly impacts performance. However, there remain challenges in this task: 1) measurement precision in large scope; 2) larger ranges and flexibility in complex surface test; 3) environmental robustness in applications; 4) efficiency and accuracy in data processing. This study introduces a novel Multi-Wavelength Point Diffraction Interferometry (MPDI) method, significantly enhancing measurement flexibility and accuracy. Through the diffraction, high-accuracy wavefront (λ/10^-4) is produced to perform relative measurement to aspherical mirrors. By integrating a triple-wavelength laser module and utilizing the beat frequency concept, the system generates at least nine equivalent wavelengths (245.8 nm to 3334.2 nm), enabling efficient testing of mirrors with both large surface deviations and high-resolution requirements. A key innovation is the random two-step phase retrieval method, which improves measurement efficiency by nearly 60% compared to conventional four-step methods, while minimizing the effects of environmental disturbances. The proposed system, equipped with machine vision alignment, ensures precise optical path alignment and enhances wavefront quality. Experimental results show a 5.3-fold increase in measurement range and RMS errors as low as 0.6∙10^-3λ (λ = 633 nm), with stitching-free testing. This MPDI method offers substantial improvements in measurement range, robustness, and efficiency, making it a valuable tool for precision aspherical mirror metrology.