Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

High precision interferometric measurement of freeform surfaces from the well-defined sub--aperture surface profiles

Sangwon Hyun1,a, I-Jong Kim1, Minwoo Jeon1, Geon-Hee Kim2 and Kye-Sung Lee1

11 Department of Scientific Instrumentation, Korea Basic Science Institute, 169-148 Gwahak-ro, Yuseong--gu, Daejeon, South Korea

2Department of Mechanics-Materials Convergence System Engineering, Hanbat University, 125 Dongseo-daero, Yuseong-gu, Daejeon, South Korea


We report an interferometric method for smooth freeform optics from the amount of sub-aperture surface profiles. The overall experimental system is composed of a 5-axis precision stage and a sub-aperture measuring interferometer, which is carefully calibrated to achieve 2 nmRMS precision. The sub-aperture interferometer adopts a broadband source in order to maximize the reliability of profile measurement, and a preliminary assumption of the overall surface is derived from the measured local 2nd derivatives which is robust to tip/tilt alignment errors during the sub-aperture acquisition. The optical surface of a 200 mm diameter 2D polynomial freeform mirror is measured based on this system and traditional contact surface profiler for the cross-validation. The experiment shows the effectiveness of the system that the mismatch against a commercial interferometer is less than 20 nmRMS.

Keywords: Interferometry, Freeform, Subaperture stitching

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