The innovation is a new, non-contact approach for sensing the local surface height of an optic. It offers an unprecedented combination of features: (1) sub-nanometer sensitivity and accuracy without calibration; (2) large dynamic range (several mm or more); and (3) accommodates large surface slopes and structure. The proposed approach vastly increases the dynamic range of conventional focusing interferometers and yet the sensitivity and accuracy are preserved at their sub-nanometer level. In a secondary innovation, an optical aberration is added to enlarge the focused spot on the test piece for immunity to surface defects. The aberration is exactly cancelled on the return trip from the test piece, thus maintaining wavefront quality and measurement accuracy. These innovations can greatly improve the optical profiling of astronomical and space optics. Bauer recently demonstrated an extremely successful optical aspheric profilometer under a NASA SBIR contract. This nanometer-level profilometer could benefit greatly from this vastly increased dynamic range afforded by these new innovations. POTENTIAL COMMERCIAL APPLICATIONS An instrument derived from the currently proposed project would be capable of measuring surface figure of large and small concave or convex aspheres with large aspheric departures, and would therefore be of great interest to much of the precision optics community. One important application is extreme ultra violet or 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
