Experimental verification of dispersed fringe sensing as a segment phasing technique using the Keck Telescope

摘要

Dispersed Fringe Sensing (DFS) is an efficient and robust method for coarse phasing of segmented primary mirrors (from a quarter of a wavelength up to the depth of focus of a single segment, typically several tens of microns). Unlike phasing techniques currently used for ground-based segmented telescopes, DFS does not require the use of edge sensors to sense changes in the relative heights of adjacent segments; this makes it particularly well-suited to the phasing of space-borne segmented telescopes, such as the James Webb Space Telescope (JWST). In this work we validate DFS by using it to measure the pistons of the segments of one of the Keck telescopes; the results agree with those of the Shack-Hartmann based phasing scheme currently in use at Keck to within 2% over a range of initial piston errors of +-16 μm.