A novel plasma-assisted atomistic surface finishing on freeform surfaces of fused silica

Abstract

A novel non-contact type plasma-assisted atomistic surface finishing of freeform surface on a fused silica is conceived. The developed process is targeted to obtain ultrafine surface finish while eliminating the surface and subsurface damages. Stable plasma with He and Ne processing gases and O2 and SF6 reactive gases up to 30 mbar pressure is achieved by using dielectric barrier capacitive coupled RF discharge. Atomic emission spectroscopy is used to identify the relative density of the excited species in the plasma to study the atomistic material removal mechanism. On machined fused silica surface, improvement in surface roughness is up to 68% with He-O2 plasma while there is 85% improvement in surface waviness. Further surface finish improvement is achieved with He-SF6-O2 gas mixture plasma with 0.008 mm³/min material removal rate. Atomistic material removal has also enabled reduction in surface residual stresses and surface cracks thereby enhancing the surface integrity.