Mechanism Of Optical Surface Machining In Plasma

With the development of optics and its related technology, especially the short wave optics and high power laser technology, the surface roughness of optical elements are required to be less than 1nm and the surface and sub-surface damage are forbidden. The optical surface machining in plasma is an emerging and potential super smooth surface processing technology.Based on the plasma machining equipment, the effects of different surface treatment technology and surface condition on removal rate and surface roughness are studied. The relationship between the removal rate and experimental parameters are analyzed, including gas flow rate, RF power, magnetic intensity and polishing time. The relations between plasma characteristic and removal rate and surface roughness are defined. The machining mechanism of optical surface using plasma is preliminary revealed.The results of this research are given as follows. The machining effects are better in using 100MHz plasma source than in 13.56MMHz. The removal rate shows a peak value with the O2 mass flow increasing. However,it linearly increases with the increase of RF power and magnetic intensity. The optical surface roughness initially increases, and then monotonically decreases with the increase of O2 mass flow. Moreover, the optical surface roughness also decreases with the increase of RF power and magnetic intensity. There are obvious removal amounts until 20min polishing, and then the removal amounts increase linearly with the polishing time. The surface roughness decrease before the polishing time is 80min and increase with the polishing time more than 80min. The removal rate and surface roughness varies with different surface condition. When spinning glycol ether on the substrate, the removal rate reaches maximum value of 6.7nm/min and the surface roughness is up to minimum value of 0.83 nm (RMS).