Magnetically controlled homogenised plasma-assisted mechanochemical lapping of calcium fluoride optical components

Abstract

Calcium fluoride (CaF₂) optical components are ideal candidates for potential applications in Inertial Confinement Fusion megascience facilities. However, their high brittleness and chemical inertness pose significant challenges in achieving uniformity and near-damage-free processing for large-aperture optical elements. To address this, this study innovatively employs magnetron-controlled H₂O(g) plasma to homogeneously modify CaF₂ surfaces, effectively reducing material brittleness and expanding the ductile-domain machinable scale. A strategy integrating strongly oxidative mechanochemical lapping tools is proposed, enabling contact-based chemical modification followed by soft abrasive removal, thereby realizing high-precision flattening of large-aperture optical components. Through multiscale simulations and experimental validation, the mechanisms of magnetron plasma homogenization and mechanochemical lapping-induced surface generation are systematically elucidated. Results demonstrate that the magnetron plasma-modified layer exhibits excellent uniformity with a modification depth of approximately 50 nm. After oxidative composite abrasive mechanochemical lapping, the plasma-modified layer is preferentially removed at an enhanced efficiency of 172 nm/min without introducing secondary damage. The processed CaF₂ surface achieves a surface roughness of 1.1 nm. This research propels the application of magnetically controlled homogenized plasma modification technology in ultra-precision machining, establishing critical technical support for processing advanced optical components.