What's it about?

Freeform applications are growing and include helmet-mounted displays, conformal optics (e.g. windows integrated into airplane wings), and those requiring the extreme precision of EUV. These 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. We will discuss the total manufacturing process, including generation, pre-polishing, MRF®, and metrology, highlighting the capabilities available in today’s optical fabrication companies.

Non-rotationally symmetric freeform surfaces are becoming more common in optical systems and are driving a need for better polishing and metrology techniques. Lack of symmetry, along with rapidly varying local slope and curvature, increase the challenges during all aspects of fabrication. Recent advances in polishing and metrology have addressed many of these difficulties, and the manufacture of freeform surfaces is possible today. In addition to the increased complexity that these surfaces cause for manufacturing, challenges also exist with the definition of the nominal surface, tolerancing, proper best-fitting of the nominal shape to the measured shape, and final analysis against the specification. Similar challenges have existed with aspheres and will only become more important with freeform surfaces...