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Chromatic effects in narrowband phasing of the Keck Telescope segments: theory and numerical simulations
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Paper Abstract

The narrowband segment phasing algorithm that was originally developed at Keck was replaced many years ago by a broadband algorithm that, although slower and less accurate than the former, has proved to be much more robust. A thorough investigation into the lack of robustness of the narrowband algorithm has now shown that this results from systematic errors (∼ 20 nm on average) that are wavelength-dependent. We show that the seemingly continuous distribution of these chromatic errors in fact results from (at least) two independent causes. The largest and most problematic effects are due to “plateaus” of unremoved material that were covered by supports during the ion beam figuring of three of the segments, but other smaller chromatic effects are also shown to be present and these are not yet understood. If the purely chromatic effects can be eliminated, we show that the intrinsic accuracy of the narrowband algorithm is about 6 nm (surface).

Paper Details

Date Published: 6 July 2018
PDF: 11 pages
Proc. SPIE 10700, Ground-based and Airborne Telescopes VII, 107001E (6 July 2018); doi: 10.1117/12.2310157
Show Author Affiliations
Gary Chanan, Univ. of California, Irvine (United States)
Mitchell Troy, Jet Propulsion Lab. (United States)


Published in SPIE Proceedings Vol. 10700:
Ground-based and Airborne Telescopes VII
Heather K. Marshall; Jason Spyromilio; Roberto Gilmozzi, Editor(s)

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