28 July 2010 Setting up ELP-OA: the polychromatic laser guide star demonstrator
Author Affiliations +
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.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
N. Meilard, N. Meilard, R. Foy, R. Foy, M. Langlois, M. Langlois, M. Tallon, M. Tallon, E. Thiébaut, E. Thiébaut, A. Petit, A. Petit, A. Blazit, A. Blazit, P.-E. Blanc, P.-E. Blanc, J. Chombart, J. Chombart, O. Fouche, O. Fouche, A. Laloge, A. Laloge, A. Le Van Suu, A. Le Van Suu, X. Regal, X. Regal, J. Schmitt, J. Schmitt, M. Boër, M. Boër, } "Setting up ELP-OA: the polychromatic laser guide star demonstrator", Proc. SPIE 7736, Adaptive Optics Systems II, 77361W (28 July 2010); doi: 10.1117/12.858068; https://doi.org/10.1117/12.858068


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