Ion-beam machining of millimeter scale optics

An ion-beam microcontouring process is developed and implemented for figuri ng millimeter scale optics. Ion figuring is a noncontact machining techniqu e 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 thi s noncontact mode of material removal, problems associated with tool wear a nd edge effects, which are common in conventional machining processes, are avoided. Ion-beam figuring is presented as an alternative for the final fig uring of small (<1-mm) optical components. The depth of the material remove d by an ion beam is a convolution between the ion-beam shape and an ion-bea m dwell function, defined over a two-dimensional area of interest. Therefor e determination of the beam dwell function from a desired material removal map and a known steady beam shape is a deconvolution process. A wavelet-bas ed algorithm has been developed to model the deconvolution process in which the desired removal contours and ion-beam shapes are synthesized numerical ly 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 a lgorithm 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 (similar to 200-mu m FWHM) ion beam. T his 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-dimensiona l sinusoidal depth profile in a prepolished silicon substrate. This profile was figured to within a rms error of 25 nm in ore iteration. (C) 2000 Opti cal Society of America.