The OptiPro Nanometric Probe is a spectral chromatic interferometer that can measure the displacement to a surface, such as an astronomical telescope mirror, with outstanding performance. Indeed, in Phase I we designed and built a Probe that demonstrated 0.48nm repeatability (one sigma). When scanned across the surface of the mirror a full topographical map of the surface – and its surface errors – can be produced.
While the Phase I probe could only operate at rates of 10 measurements/second, we have developed optical power budget spreadsheets that model how 10,000 measurement can eventually be reached with currently available off-the-shelf components. Furthermore, the Probe is generally not light-limited, and we believe that it can function with the weak back-scattered (non-specular) light from highly-polished highly-tilted surfaces, although this assertion will be tested in Phase II.
Other work proposed in Phase II for the Nanometric Probe is directed at improving the current performance of the Probe to a level consistent with its full performance expectations. In particular, the Probe’s light throughput and align-ability will be improved substantially. With light throughput improvement we also expect to see a corresponding improvement in the Probe’s signal-to-noise ratio, which we are hopeful will reduce the Probe’s measurement uncertainty five-fold to less than 100 picometers (one sigma).
Also, other factors limiting the measurement rate of the Probe, such as the capture rate of the spectrometer and the processing speed of the digital hardware, will be upgraded so that a rate of 1000 measurements/second can be achieved by the end of Phase II. Finally, infrastructure will be procured and installed so that the Probe’s displacement measurements can be calibrated, and the Probe’s performance over its full operational envelope can be characterized.
The Nanometric Probe is ideal for mirror surface error (including mid-spatials) metrology of HabEx and LUVOIR missions, as well as X-Ray missions such as Lynx and AXIS. In each case the measurement uncertainty of the Probe is expected to be less than 10% of the surface error budget of the mirror being measured. The usage of the Probe in such applications requires that the Probe is mounted on a high-performance CMM so the Probe's position above the mirror is known. The ANCMM featured in a co-pending Phase II proposal meets that requirement.
Researchers in the field of synchrotron X-Ray generation at Argonne National Labs have discovered our activities in nanometric metrology, and we have had in-depth conversations with them about X-Ray mirror metrology. The Nanometric Probe can also be applied to the measurement of aspheric optics used in the lithography industry in which the surface error tolerances are often less than 2nm RMS.