Synergistic processing of fused silica by atmospheric pressure microwave plasma etching and small tool conformal polishing

The high-performance fabrication of fused silica optical components faces the core challenge of achieving high efficiency and low damage in removing processing-induced defects while simultaneously improving form accuracy and surface roughness. To address this bottleneck, this paper proposes a novel synergistic processing strategy combining atmospheric pressure microwave plasma (APMP) etching with conformal polishing using a small tool. The processing mechanism is as follows: under optimized conditions, APMP exhibits a high material removal rate, and its low thermal/mechanical stress characteristics enable effective removal of surface and subsurface defects introduced by grinding while correcting form errors. However, the isotropic nature of plasma etching leads to surface roughness degradation. Subsequently, conformal polishing with a small tool selectively smooths microscopic peaks through a “gentle” material removal mechanism without introducing new subsurface damage or scratches, and conforms to the local surface topography, thereby repairing the deteriorated roughness while preserving the form accuracy corrected by the plasma step. The two processes complement each other, balancing high removal efficiency and high surface quality. Using the proposed synergistic process, the form error RMS of a fused silica mirror was reduced from 38.01 nm to 9.03 nm, and the average surface roughness Sa was reduced from 0.811 nm to 0.322 nm. Verification by buffered oxide etch (BOE) confirmed that the final component is free of subsurface damage. The results demonstrate that the synergistic processing method combining APMP etching and conformal polishing with a small tool is a promising approach for ultra-precision surface machining of fused silica glass.