Shanbhag P M, Feinberg M R, Sandri G, Horenstein M N, Bifano T G
Photonics Center, Boston University, Boston, Massachusetts 02215, USA.
Appl Opt. 2000 Feb 1;39(4):599-611. doi: 10.1364/ao.39.000599.
An ion-beam microcontouring process is developed and implemented for figuring millimeter scale optics. Ion figuring is a noncontact machining technique in which a beam of high-energy ions is directed toward a target substrate to remove material in a predetermined and controlled fashion. Owing to this noncontact mode of material removal, problems associated with tool wear and edge effects, which are common in conventional machining processes, are avoided. Ion-beam figuring is presented as an alternative for the final figuring of small (<1-mm) optical components. The depth of the material removed by an ion beam is a convolution between the ion-beam shape and an ion-beam dwell function, defined over a two-dimensional area of interest. Therefore determination of the beam dwell function from a desired material removal map and a known steady beam shape is a deconvolution process. A wavelet-based algorithm has been developed to model the deconvolution process in which the desired removal contours and ion-beam shapes are synthesized numerically as wavelet expansions. We then mathematically combined these expansions to compute the dwell function or the tool path for controlling the figuring process. Various models have been developed to test the stability of the algorithm and to understand the critical parameters of the figuring process. The figuring system primarily consists of a duo-plasmatron ion source that ionizes argon to generate a focused (approximately 200-microm FWHM) ion beam. This beam is rastered over the removal surface with a perpendicular set of electrostatic plates controlled by a computer guidance system. Experimental confirmation of ion figuring is demonstrated by machining a one-dimensional sinusoidal depth profile in a prepolished silicon substrate. This profile was figured to within a rms error of 25 nm in one iteration.
一种用于加工毫米级光学元件的离子束微轮廓加工工艺被开发并实施。离子加工是一种非接触式加工技术，其中高能离子束被导向目标基板，以预定和可控的方式去除材料。由于这种非接触式材料去除模式，避免了传统加工工艺中常见的与刀具磨损和边缘效应相关的问题。离子束加工被提出作为小尺寸（<1毫米）光学元件最终加工的一种替代方法。离子束去除的材料深度是离子束形状与在二维感兴趣区域上定义的离子束驻留函数之间的卷积。因此，从期望的材料去除图和已知的稳定束形状确定束驻留函数是一个反卷积过程。已开发出一种基于小波的算法来对反卷积过程进行建模，其中期望的去除轮廓和离子束形状被数值合成为小波展开。然后我们通过数学方法组合这些展开式来计算驻留函数或控制加工过程的刀具路径。已开发出各种模型来测试算法的稳定性并了解加工过程的关键参数。加工系统主要由一个双等离子体离子源组成，该离子源使氩气电离以产生聚焦（半高宽约200微米）的离子束。该束通过由计算机引导系统控制的一组垂直静电板在去除表面上进行光栅扫描。通过在预抛光的硅基板上加工一维正弦深度轮廓来证明离子加工的实验验证。该轮廓在一次迭代中被加工到均方根误差在25纳米以内。
