Chromatic Interferometric Probe

Proposed herein is a novel non-contact chromatic phase-measuring interferometric probe capable of measuring the surface form of a free-form telescope optic to nanometer, or even sub-nanometer, levels. The probe retains all the benefits of a chromatic optical probe (i.e., large measurement range and small spot size) as well as the benefits of a phase-measuring interferometer (i.e., high accuracy and repeatability, and speed). The probe has been computer simulated, and it seems entirely feasible to expect measurement standard deviations of 0.9 nanometers (over 1mm measurement range in the Z-axis), at a rate of 10,000 data points per second, on ground or polished surfaces, on perpendicular or sloped (up to 60°) surfaces, with a 10 micron probe spot size. These metrology performance characteristics are required such that the metrology uncertainty does not consume an inordinate percentage of the 8nm (RMS) form error of UVOIR-caliber space telescope optics. In the proposed Phase I effort we will endeavor to mitigate the risks we have identified with the probe, such as verification of the optical power budget, and confirming that the optical output signal has the anticipated structure and brightness by assembling a probe for demonstration purposes. Finally, baseline repeatability performance will be established by characterizing the probe in an environmentally controlled test chamber at the University of North Carolina at Charlotte.

The proposed metrology system can be used for sub-nanometer surface metrology of free-form optical components with large spherical departures, such as the optics for X-Ray telescopes, and, especially, for UVOIR telescope optics.

Non-destructive sub-surface metrology. Optical coherence tomography of industrial and biomedical specimens.

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