Wavefront-Based Error Calibration for Coordinate Measuring Machines in the Surface Metrology of Large Optics

Abstract

Precise measurement of large mirrors is essential for high-performance space-based optics. Traditionally, laser interferometry provides high accuracy but faces challenges related to the requirements of computer-generated holograms (CGHs) and the transformation of standard wavefronts to match complex test surfaces. This paper presents a proof-of-concept contact-based surface metrology method for large mirrors. To reduce drift errors caused by stylus instability or contact loss, a wavefront-based calibration method was developed to suppress measurement artifacts while preserving intrinsic surface errors. The method was tested on a concave aspherical mirror using a tactile coordinate measuring machine (CMM), and its accuracy was evaluated by comparing deviations between calibrated CMM error maps and laser-based measurements. Experimental results demonstrated that the XENO CMM achieved a global metric accuracy comparable to interferometric systems for relevant geometric parameters. These findings suggest that ultra-precision CMMs combined with focus point calibration can provide practical preliminary surface verification and serve as a flexible alternative to laser interferometry when global geometric accuracy is the primary concern. Future work will enhance robustness by addressing higher-order aberrations.