ASPHERIZING THE SPHERE: USING FOCUSED ION BEAM MACHINING TO CREATE ASPHERICAL DIAMOND MILLS FOR MICRO OPTICS

摘要

Sandia National Laboratories has developed a method for using diamond mills to fabricate arrays of convex aspherical micro-optics. The optics are on the surface of a 2 mm radius hemisphere and have a 420 μm radius and a 660 μm diameter aperture. Conventional diamond tool production methods can create mills with spherical concave cutting edges (actually cylindrical when considering the clearance angle). However, when a design requires an asphere, there are not many options. Focused Ion Beam (FIB) shaping in combination with ultraprecision machining has been demonstrated to produce micro-scale components in a variety of materials. We procured concave, spherical diamond mills and utilized focused ion beam shaping to modify the tool geometry into an aspherical mill.rnIn fabricating the asphere on the diamond mill, there are many steps of the process from design to final part. The most significant include optical design of the aspheres, selection of a best fit radius, spherical tool manufacturing, optical redesign to utilize the actual tool radius, FIB process planning, FIB shaping, and ultraprecision machining of the desired optics using the new tool. In this report we describe each of these steps. As expected, we found that the accuracy of the final optics was dependent on the errors within each of the fabrication steps.