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Proceedings Paper

Setting up ELP-OA: the polychromatic laser guide star demonstrator
Author(s): N. Meilard; R. Foy; M. Langlois; M. Tallon; E. Thiébaut; A. Petit; A. Blazit; P.-E. Blanc; J. Chombart; O. Fouche; A. Laloge; A. Le Van Suu; X. Regal; J. Schmitt; M. Boër
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Paper Abstract

ELP-OA ('Etoile Laser Polychromatique pour l'Optique Adaptative) aims at demonstrating the tip-tilt is measurable with a Laser Guide Star (LGS) without any natural guide star. This allows a full sky coverage down to visible wavelengths. ELP-OA is being setup at Observatoire de Haute-Provence (OHP). To create a polychromatic LGS, we use two pulsed dye lasers (at 569nm and 589nm) to produce a two-photons excitation of sodium atoms in the mesosphere. The chromatism of the refractive index of the air yields a difference of the LGS direction at different wavelengths. The position differences is proportionnal to the tip-tilt. Since the LGS isn't sharp enough to give us a small enough error in the differential tip-tilt, we use an interferometric projector to improve the high spatial information in the laser spot. It requires an adaptive optics working down to 330nm. This one is done by post-processing algorithms. Two two aperture projectors are used. Each one creates a fringe-modulated LGS, and a better RMS error in the LGS position is obtained by measuring the information in a normal direction with respect to the fringes. By using a two aperture projector, we also strongly decrease the negative effect of the laser star elongation in the mesosphere, and the Rayleigh contribution near the LGS. We propose a new optimal algorithm to retrieve the tip-tilt from simultaneous images at different wavelengths. To enhance the RMS error of the measurements, we extend this algorithm to exploit the temporal correlation of the turbulence.

Paper Details

Date Published: 28 July 2010
PDF: 9 pages
Proc. SPIE 7736, Adaptive Optics Systems II, 77361W (28 July 2010); doi: 10.1117/12.858068
Show Author Affiliations
N. Meilard, Univ. de Lyon (France)
Observatoire de Lyon, Univ. Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
R. Foy, Univ. de Lyon (France)
Observatoire de Lyon, Univ. Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
M. Langlois, Univ. de Lyon (France)
Observatoire de Lyon, Univ. Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
M. Tallon, Univ. de Lyon (France)
Observatoire de Lyon, Univ. Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
E. Thiébaut, Univ. de Lyon (France)
Observatoire de Lyon, Univ. Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
A. Petit, Commissariat à l'Énergie Atomique (France)
A. Blazit, Observatoire de la Côte d'Azur (France)
P.-E. Blanc, Observatoire de Haute-Provence, CNRS (France)
J. Chombart, Observatoire de Haute-Provence, CNRS (France)
O. Fouche, Observatoire de Haute-Provence, CNRS (France)
A. Laloge, Observatoire de Haute-Provence, CNRS (France)
A. Le Van Suu, Observatoire de Haute-Provence, CNRS (France)
X. Regal, Observatoire de Haute-Provence, CNRS (France)
J. Schmitt, Observatoire de Haute-Provence, CNRS (France)
M. Boër, Observatoire de Haute-Provence, CNRS (France)


Published in SPIE Proceedings Vol. 7736:
Adaptive Optics Systems II
Brent L. Ellerbroek; Michael Hart; Norbert Hubin; Peter L. Wizinowich, Editor(s)

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