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Building the demonstrator of the Polychromatic Laser Guide Star (ELP-OA) at Observatoire de Haute-Provence (OHP)

Abstract 130

Submitted by Renaud FOY


R. Foy (1), P.-É. Blanc (2), T. Fusco (3), A. Laloge (2), A. LeVanSuu (2), N. Meilard (1), S. Perruchot (2), A. Petit (4), M. Tallon (1), É. Thiébaut (1), M. Boër (2)


(1) CRAL / Observatoire de Lyon; (2) OHP; (3) ONERA; (4) CEA


We report the status of ELP-OA (Étoile Laser polychromatique pour l’Optique Adaptative), the full demonstrator which we are building at OHP 1.52m telescope. The goal is to open adaptive optics to the domain of visible wavelengths at large telescopes, which is almost not feasible today because of the tiny isoplanatic patch.

ELP-OA relies on the 2-photon excitation of sodium in the mesosphere, through 589 and 569 nm transitions. We use 2 pulsed dye lasers (on loan from the French agency CEA) pumped with NdYAGs. The average power at the mesosphere will be 2x22W. The twin laser beams are projected to the mesosphere by a 3-aperture interferometer. The backscattered spot in NaI lines at 330, 569 and 589nm is oberved through an adaptive optics bench at the telescope coudé focus. It is close to the ONERA’s BOA device, except that :

- its optical throughput is optimized for 330nm,

- telescope vibrations measured by a Tokovinin’s pendular seismometer are corrected in open loop by the tip-tilt mirror

- the tilt is measured from its derivative between 569 and 330nm - the wavefront sensor is fed by the 589nm light

The differential tilt measurement channel is equipped with an EMCCD. We use a correlation algorithm to extract it.

From our end to end model we expect tilt Strehl ratios of 35% at 550nm (see Meilard et al in this conference).

First lasers launches are planned early 2010, with the full experiment starting to run beginning of 2011.

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