NASA 1996 SBIR Phase I

PROJECT TITLE : Multi-point in-situ profiling of large aspherics

TECHNICAL ABSTRACT (LIMIT 200 WORDS)

The innovation is a new approach for measuring the surface figure of large aspheric optical surfaces. Our approach is an optical profiler using multiple sensors in an innovative configuration to achieve self-referencing operation. The sensors are mounted together on a rigid, common turntable. As we impart a compound rotary motion to the turntable (one motion rotates the sensors about a common axis, and the second motion rotates this center of rotation about the center of the test piece), we simultaneously measure the proximity of the optical surface from each sensor. The result, after sophisticated analysis, is a map of the surface asphericity. The measured surface map is independent of any small rigid body motions of the sensor framework (vibrations, wobbles, etc.), and does not rely on any reference surface. Other important features include small size - the instrument is comparable in size to the optic being tested, rather than to its radius of curvature (which can be many times larger than the optic itself). Also, it is equally applicable to convex and concave surfaces, and there is essentially no limitation on the speed (F-number) of the test piece. These are important advantages over approaches such as interferometers and Hartmann testers, and allow in-situ testing. Potential NASA applications include measurement of the Next Generation Space Telescope (NGST) primary and secondary mirror surfaces.

An instrument derived from the currently proposed project would be capable of measuring surface figure of large and small aspheres, and would therefore be of great interest to much of the precision optics community. One important application is soft X-ray projection lithography, where absolute profiling of very smooth aspheres is critical. Thus, this project would be of interest both to the commercial optics and semiconductor manufacturing communities.

Paul Glenn,
Bauer Associates, Inc.
888 Worcester Street, Suite 30,
Wellesley, MA 02181

Bauer Associates, Inc.
888 Worcester Street,
Suite 30, Wellesley, MA 02181