The project is to assess the feasibility of a new approach to profiling nearly flat optical surfaces. It builds on another innovative profiling technique that measures local surface curvatures and numerically processes the data to yield a profile. In the new proposed approach, we significantly change the optical configuration so that local surface slopes are measured, rather than local surface curvatures. Local slopes are measured with respect to the test piece itself, rather than with respect to the measurement instrument. In this way, the measurement is completely self-referencing, so that drifts of the instrument with respect to the test piece have no effect on the accuracy. The measurement of slope allows for the measurement of absolute departure from a flat. Such a measurement approach would be of great benefit to a variety of telescopes, interferometers, and related systems, especially in the X-ray regime, both because of the ability to measure absolute flatness and because of the ability to measure over unprecedented scan lengths.The potential applications of a long-scan profiler with absolute flatness capabilities are numerous. Absolute flatness is a critical parameter in many metrology applications common to all large optical shops. Moreover, measurements of figure quality over long scan lengths (100 mm to 1000 mm) is difficult. Accuracies in the 1 to 10 nm-class that appear to be possible with our modified slope profiling would be a great help in the characterization of large, nearly flat optics. In short, large laboratories working in optical fabrication and metrology would have a need for the long scan, high accuracy profiles that would be possible with a successful Phase II instrument.
