A novel and efficient multi-jet plasma polishing process for optical fabrication

Abstract

There is an increasing demand for higher precision, larger sizes, and greater machining efficiency for freeform optical elements due to the rapid development of advanced optics. Plasma processing technology has gained significant attention due to its capability for damage-free and high-precision optical fabrication; however, achieving high processing efficiency for medium- to larger-aperture optical elements remains a challenge. This paper proposes a novel multi-jet polishing process based on the atmospheric pressure plasma jet (APPJ), capable of high-efficiency deterministic optical polishing. First, the uniformity of the proposed tool was verified through spatial electric field simulations, and the electrode size parameters were further optimized to ensure uniformity and stability. Subsequently, etching experiments were conducted to optimize the relevant process parameters, achieving stable and efficient material removal. The volumetric removal rate increased to 9.4 times that of the conventional small-size single APPJ process, which was greater than the increase in the number of processing units. Then the surface generation mechanism was analyzed, verifying that the proposed process can effectively mitigate mid-spatial frequency errors induced by periodic tool path. Finally, a fused silica window with a form error of PV 111.6 nm and RMS 16.63 nm was achieved through the deterministic polishing experiment and the processing efficiency is nearly 9 times higher than that of a single APPJ, which shows that the proposed multi-jet plasma polishing process is an efficient, high-precision and stable optical fabrication process. The number of processing units could be increased from a few to dozens by extending the periodic array of single-unit APPJs, thus demonstrating significant potential for the optical fabrication of medium- to large-aperture elements.