Extended range profiling

We analyze a new, noncontact approach for sensing the topography of an optic. It offers (1) sub-nanometer accuracy; (2) several mm or more of dynamic range; and (3) accommodation of large surface slopes and structure. We add autofocusing to a focusing distance measuring interferometer to keep the beam focused on the test piece. The measurement is unaffected by small autofocusing errors. Thus, the range is extended to the lens-servoing range; the servoing has loose tolerances; and the sub-nanometer accuracy is preserved. In another innovation, we add coma (by tilting the lens) to enlarge the focused spot on the test piece to be immune to surface defects. The coma is canceled on the return trip through the lens, preserving wavefront quality. These innovations can greatly improve the optical profiling of astronomical and space optics.Our Phase I project was successful - we arrived at a workable design including mechanics, optics, actuation, and servoing architecture. In Phase II we have two main technical (and programmatic) objectives: (1) develop and demonstrate a potentially commercially viable extended range probe; and (2) use a set of those probes in a specific instrumental configuration to demonstrate explicitly the ability to perform sub-nanometer profilometry.