光学元件离子束修形去除效率分析

离子束修形(IBF)技术成为光学零件获得超高面形必不可少的加工工艺.修形过程中采用光阑获取小的束径、稳定的去除函数是获得超高面形精度的前提.不同材料和工艺参数等不同条件下获得的去除函数都不相同,每次修形前都要重新测量去除函数.研究了不同入射能下、不同靶距下以及有无光阑时去除函数的变化.发现在离子光学系统几何参数一定的条件下,离子束去除函数的效率变化与入射能量、离子体浓度引起的离子鞘形状、束散角、温度、靶距、净加速电压与总加速电压之比的变化等因素都有关.当增大入射能量时,去除效率随之增加,但当入射能量大于一定值后就会出现随着入射能量增加而去除效率降低的"拐点"现象.有无光阑只改变去除效率的大小而不会改变"拐点"现象.因此不选用入射能量增大而去除效率减小的"拐点"之后的入射能量修形.

Analysis of Removal Efficiency of Ion Beam Figuring for Optical Component

Ion beam figuring （IBF） has been considered essential in modem advanced optical component manufacturing process. Using diaphragm to get small-diameter ion beam and choosing steaty removal function is the premise to achieve high surface accuracy in ion beam figuring process. Different materials, process parameters, and environmental conditions lead to different removal functions. Every time before figuring, it is necessary to get removal function and look for better process parameters to improve the figuring effect. This paper examined the effect of incident energy, target distance, and diaphragm on removal efficiency. Results indicate that, in a definite ion optical system, ion beam removal efficiency varies with ion incident energy, ion density, ion beam divergence angle, temperature, target distance, ratio of accelerating voltage and total voltage difference. Removal efficiency increases with the increase of incident energy, but it will begin to decrease when the incident energy reaches a ＂flex point＂. The diaphragm affects removal efficiency but will not change the ＂flex point＂. When we get the removal function, it is not reasonable to figure with incident energy after ＂flex point＂ when the incident energy increases while removal efficiency decreases.