On-machine measurement for ultra-precision single-point turning of large-aperture micro-optical elements based on white-light interferometry

Large-aperture micro-optical elements are crucial in fields such as semiconductor lithography and astronomy. Owing to their extremely high manufacturing precision, sophisticated surface topography detection methods are required. White-light interferometry is one of the most accurate 3D surface topography measurement technologies, with measurement noise less than 0.1 nm. However, traditional off-line measurement not only has low efficiency but also introduces repeated clamping errors, affecting the final machining accuracy. An in-situ white-light interference measurement system is developed and directly integrated into a five-axis ultra-precision lathe, enabling high-precision on-machine measurement of large-aperture micro-structured optical elements. While achieving miniaturization, the system’s performance indicators such as measurement noise and flatness are comparable to commercial white-light interferometers. Additionally, by establishing an on-machine measurement kinematic model and combining it with the workpiece CAD model for measurement alignment, the on-machine white-light interferometer system successfully realizes full-aperture measurement of grating structures and mid-frequency roughness of large-aperture micro-structured optical elements. This approach significantly improves measurement efficiency while ensuring accuracy, providing real-time and high-precision topography detection for manufacturing high-end optical elements such as large-aperture micro-structured optical components.