Field proven technologies for fabrication of high-precision aspheric and freeform optical surfaces

Abstract

The subaperture and conformal nature of the MRF® polishing tool has proven its unmatched production capability and efficiency for more than a decade at leading optics manufacturers worldwide. The introduction of the third generation of manufacturing systems combined with newly developed MRF fluids pushes the limits of the technology to extend its benefits to very low roughness surfaces and high-precision freeform surfaces. In this article, after reviewing the benefits of the new platforms, two specific examples of very advanced capability will be discussed: - A new super-fine MRF polishing fluid that is able to meet both form and roughness specifications for very demanding optics required for EUV applications and high power laser systems. EUV optics, made of calcium fluoride or similar materials, ideally require sub-Angstrom surface roughness while achieving nm level form error. To achieve the above specifications, optics must undergo iterative global and local polishing processes. The new MRF polishing fluid minimizes the number of steps required if MRF® is used as the final step, or a reduction in the post-processing if a final smoothing step is performed. - The total manufacturing process, including generation, pre-polishing, MRF and metrology, of a very steep freeform surface, highlighting the capabilities available in today’s optical fabrication companies. Non-rotationally symmetric surfaces pose challenges to optical fabrication, mostly in the areas of polishing and metrology. The varying curvature of freeform surfaces drives the need for smaller, more “conformal” tools for polishing and reference beams for interferometry. In this paper, we present the fabrication results of a high-precision freeform surface.