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Proceedings Paper

Phase diversity experiment to measure piston misalignment on the segmented primary mirror of the Keck II Telescope
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Paper Abstract

We are developing a technique to measure segment misalignment of large telescopes based on wavefront estimation using phase-diverse images. We report the current results of an experiment to measure piston errors on the Keck II primary segmented mirror, through atmospheric turbulence, using phase-diverse phase retrieval. The segment piston errors are separated from the random turbulence by averaging phase estimates from many frames. Phase estimates from real data collected with segments intentionally moved in piston reproduce the observed speckle patterns well. However, average phase maps do not reveal the segment piston errors. Simulations show that the observed data were collected in a regime of turbulence where the current algorithm often fails, but would be expected to work very well when the adaptive optics system is operating. There is reason to believe that we can eventually make the algorithm work with these or similar data if apparent mismatches between the data and our current imaging model are removed.

Paper Details

Date Published: 28 August 1998
PDF: 12 pages
Proc. SPIE 3356, Space Telescopes and Instruments V, (28 August 1998); doi: 10.1117/12.324519
Show Author Affiliations
Mats G. Lofdahl, Lockheed Martin Missiles & Space (Sweden)
Rick Lee Kendrick, Lockheed Martin Missiles & Space (United States)
Alex Harwit, Lockheed Martin Missiles & Space (United States)
Keith E. Mitchell, Lockheed Martin Missiles & Space (United States)
Alan L. Duncan, Lockheed Martin Missiles & Space (United States)
John H. Seldin, ERIM International (United States)
Richard G. Paxman, ERIM International (United States)
D. Scott Acton, W.M. Keck Observatory (United States)


Published in SPIE Proceedings Vol. 3356:
Space Telescopes and Instruments V
Pierre Y. Bely; James B. Breckinridge, Editor(s)

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