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Proceedings Paper

ZEUS: a cophasing sensor based on the Zernike phase contrast method
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Paper Abstract

We describe the ZEUS phasing camera for future extremely large telescopes (ELTs) based on the Zernike phase contrast method. A prototype instrument is under construction for implementation in the Active Phasing Experiment (APE), a VLT test bed scheduled for operation in 2007. The paper describes theoretical aspects of the method and its experimental validation, as well as the instrumental implementation for APE. Aspects of its implementation in an ELT are also discussed. While the classical Zernike method uses a phase mask with diameter approximately equal to the Airy disk, we employ a mask the size of the seeing disk. This allows us to overcome the problems related to atmospheric turbulence, whose low spatial frequency phase errors are much larger than the co-phasing errors to be measured. The thickness (OPD) of the mask can be set to lambda/4 - as in the classical case - for maximum signal strength, but for initial phasing where phase errors are much larger than the sensor's linear range (+/-lambda/4), a thinner mask produces a cleaner signal more easily exploitable, leaving the signal analysis more robust. A multi wavelength approach is implemented in order to extend the capture range of the sensor, and the ultimate precision is reached using an iterative approach. End-to-end simulations indicating an achievable precision within the required precision will be shown.

Paper Details

Date Published: 23 June 2006
PDF: 11 pages
Proc. SPIE 6267, Ground-based and Airborne Telescopes, 626734 (23 June 2006); doi: 10.1117/12.671377
Show Author Affiliations
Kjetil Dohlen, Lab. d'Astrophysique de Marseille (France)
Maud Langlois, Lab. d'Astrophysique de Marseille (France)
Patrick Lanzoni, Lab. d'Astrophysique de Marseille (France)
Silvio Mazzanti, Lab. d'Astrophysique de Marseille (France)
Arthur Vigan, Lab. d'Astrophysique de Marseille (France)
Luzma Montoya, Instituto de Astrofísica de Canarias (Spain)
Elvio Hernandez, Instituto de Astrofísica de Canarias (Spain)
Marcos Reyes, Instituto de Astrofísica de Canarias (Spain)
Isabel Surdej, European Southern Observatory (Germany)
Natalya Yaitskova, European Southern Observatory (Germany)

Published in SPIE Proceedings Vol. 6267:
Ground-based and Airborne Telescopes
Larry M. Stepp, Editor(s)

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