Smoothing of fused silica with less damage by a hybrid plasma process combining isotropic etching and atom-migration

In order to effectively reduce the subsurface damage of fused silica optics and obtain an ultra-smooth surface at atomic scale, we proposed a hybrid manufacturing process based on inductively coupled plasma (ICP), which combined isotropic etching polishing (IEP) and atom-migration manufacturing (AMM). In the plasma-IEP process, a large number of isotropic etching pits with ultra-smooth inner surface formed, enlarged, overlapped and merged, resulting in a smooth surface. The continuous downward etching process was accompanied by the continuous removal of the subsurface damage layer. With optimized process parameters, plasma-IEP could efficiently generate a less damage surface of fused silica with a material removal rate of 0.8 μm/min, and reduce the Sa roughness from 97.1 nm to 31.3 nm. The surface roughness could be further reduced to less than 0.15 nm by plasma-AMM, which was a non-subtractive finishing approach. The result of laser induced damage threshold (LIDT) test showed that the fused silica surface after the IEP-AMM hybrid manufacturing could withstand higher laser fluence, which implied more effective applications of this technique in high-power laser systems. This study proposed and verified the hybrid plasma manufacturing process combining plasma-IEP and plasma-AMM, which provided an ultra-smooth surface with less damage manufacturing process for fused silica.