Fabrication of a 500 mm extreme freeform conformal window

There is a potential need for large (<500 mm diameter) conformal windows for use on air, space, and water craft. These windows need to fit the curvature of the vehicle, which results in extreme freeform geometries. "Extreme Freeforms" are a class of shapes that do not have rotational symmetry, must be polished using sub-aperture techniques, and whose deviation from a best-fit sphere is on the same order as the size of the part. This paper will discuss some of the challenges associated with manufacturing optics of this size and shape and how Optimax solved them. These challenges include: blank acquisition, a lack of viable commercially available polishing platforms for extreme freeform shapes, and metrology. A demonstrator optic was designed and manufactured from fused quartz. Final metrology data for both sides of the window will be shown and discussed.