Research on Sub-Aperture Stitching Interferometric Testing Technology for High-Steepness Mirrors Based on Instrument Transfer Function

Precise measurement of high-steepness optical components is a critical challenge currently faced, which is being overcome through a groundbreaking high-steepness mirror sub-aperture stitching interferometric measurement method utilizing the instrument transfer function (ITF). A spherical step test plate was meticulously designed and manufactured based on ITF calibration principles. This essential tool enables the calibration of the ITF distribution at different spatial positions of the sub-aperture stitching instrument during the measurement of steep spherical mirrors. A comprehensive analysis then revealed a clear ITF distribution pattern, which made it possible to develop a data fusion algorithm model for the overlapping regions in the sub-aperture stitching process. In practical application, a highly successful stitching measurement was performed on a high-steepness spherical mirror with a diameter of 100 mm and a curvature radius of 103.314 mm. The experimental results demonstrate significant improvement in optical surface metrology. The full-aperture stitching achieved a peak-to-valley (PV) residual error of 0.073λ in the central region, with a root mean square (RMS) error of 0.002λ. Similarly, the edge region exhibited a PV error of 0.039λ and an RMS error of 0.002λ. These values represent a marked enhancement over conventional averaging-based fusion algorithms. These excellent results demonstrate the effectiveness of the method proposed in this study and provide a clear solution for high-precision measurement of steep optical components. This innovative method advances the field and sets a new benchmark for the precise measurement of optical component facets.