Freeform Optics: A Non-Contact "Test Plate" for Manufacturing

The goal of this NASA SBIR Phase I study is to determine the feasibility of measuring precision (fractional wave) freeform optics using non-contact areal (imaging) optical sensors measuring slope data. Fabrication of a physical "test plate" for each freeform design is impractical and cost prohibitive. Nevertheless, surfaces must be inspected while the part is still fixed or blocked (one surface exposed). The proposed innovation is a non-contact metrology method for manufacture of precision freeform optical surfaces; a tool to play the role of the test plate in conventional optical testing. The proposed method is to be implemented as close to the CNC machine as possible to provide rapid and regular feedback to opticians throughout manufacture. Once implemented into the freeform manufacturing process, this procedure has great potential to streamline processing while increasing the manufacturing technician's information about surface condition during production. NASA and many other agencies and companies have a stated critical need for high-quality freeform optical components, and will benefit from improvements to production and testing of freeforms. Metrology is currently one gating item in the manufacturing of precision freeform surfaces.

All off-axis aspheric or non-rotationally symmetric surfaces that require high precision wavefront quality would benefit from the innovation outlined in this proposal. The optical design industry has been and continues to be interested in freeform optics, and with each new design the demand for higher precision increases. Freeform optics relevant to NASA include -the "steeply aspheric 8.4 m diameter off-axis GMT mirror" -"x-ray and UV imaging instruments on weather satellites" -a diamond machined freeform mirror in the IRMOS spectrometer at the Kitt Peak National Observatory -a three mirror telescope system -coronagraphs for exo-solar planet search These examples indicate that future NASA missions will require precision freeform optical components.

Freeform optics are quickly becoming part of many commercial and military optical systems. Many optical designers are starting to use freeform optics to achieve optical performance (less aberrations), lighter weight optical systems through a reduced number of components, and an increased ability to go off axis with smaller and tighter packages. Optimax is starting to offer commercial quality freeforms as a standard component. We are seeing designs for beam shaping, corrector plates, conformal windows, and head-up displays for example. A variety of flexible in-house metrology capabilities is necessary due to the exotic nature of the optics.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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