Development of an ion figuring system for centimeter scale optical components

An important step in the fabrication of an optical component involves the imparting of a precise contour on the optic, which can be expensive and time consuming. Ion beam figuring is the imparting of a contour on an optical component by removing material through the impingement of a broad beam of accelerated neutral particles, and provides a highly deterministic method for the final precision figuring (or correcting) of optical components with advantages over conventional methods. The high predictability allows the possibility of single step figuring, resulting in significant time and cost savings. And unlike grinding, polishing and lapping, ion figuring is non-contacting and so avoids several problems including: edge roll off effects, tool wear, and loading of the work piece. It has previously been demonstrated that ion figuring is effective for the correcting of large optical components. These implementations typically use the process for final figure correction on meter class optical components. The work discussed here is the development of the Precision Ion Machining System (PIMS) at NASA's Marshall Space Flight Center, designed for the processing of smaller (less than 10 cm diameter) optics. Initial experiments using a Kaufman type ion source to figure 8 cm diameter fused silica and silicon carbide samples were successful. Experiments involved correcting flat samples and imparting spherical and aspherical contours.