Roughness evolution of fused silica during plasma polishing processes

Abstract

Plasma polishing process finds important applications in the fabrication of super-smooth optical surfaces. It can be applied for the precise optical surface forming and to obtain optical surfaces with ultra-low roughness and without sub-surface damage (SSD). Published results show that the plasma polishing process is mainly used for the precise optical surface forming. Very limited results are reported in literatures on the process being used for the reducing of the optical surface roughness. A novel plasma polishing process has been developed in the Laboratory of Thin Film Techniques and Optical Test in Xi'an Technological University. In the process, highly stable SF 6 and Ar plasmas are generated by using capacitive coupled hollow cathode (CCHC) RF discharge method. Factors that affect the stability of the plasma, such as gas flow rate, pressure and discharge power are systematically investigated. The polishing processes of fused silica have been studied using CCHC RF plasma. When the process parameters of the gas flow, pressure, and plasma powerare optimized, the roughness of the silica surface can be reduced from 1.2nm to 1.0nm in rms with minimized SSD.

Plasma polishing processes applied on optical materials: A review

“…With increased working pressure and radio frequency power, the etching rate and the roughness of the polished surface also increases. 60 Vana et al 61 used stainless steel X10CrNi specimen for plasma polishing and observed the change in surface roughness and gloss level of the metal surface with the time variation from 0 to 600 seconds, as shown in Figure 6. Experimentally, they found much lesser surface roughness after plasma polishing with varying gloss levels during finishing, and its value depends on the finishing time.…”

“…A novel plasma polishing process was developed on fused silica for optical components. 69 This study utilizes capacitive-coupled hollow cathode RFexcited SF 6 and Ar plasma. The factors influencing the characteristics of the plasma were the rate of gas flow and power.…”