VALIDATION SUR LE CIEL DU CONCEPT D'ETOILE LASER POLYCHROMATIQUE

Abstract : The atmospheric turbulence affects image quality and causes angular resolution losses at the focus of large ground based optical telescopes. Real time adaptive optics (AO) corrects wave front distortions measured with at least one bright reference source located within a tiny isoplanatic angle from the science object. At visible wavelengths, the probability to find one such natural star is ridiculously small. The laser guide star (LGS) solves the problem but the overall wavefront slope (referred here as tilt) remains undetermined. The Polychromatic Laser Guide Star will allow the use of AO with full sky coverage. Based on the tilt chromaticity, a multicolor reference spot is created in the upper atmosphere and the differential tilt is measured between two wavelengths to retrieve the tilt itself. In the present thesis, I describe ATTILA, an experiment designed to prove the feasibility of the concept in astronomical conditions. Observations carried on at Observatoire de HauteProvence on natural stars allowed us to establish the proportionality law that links the tilt and the differential tilt for the first time. A temporal monitoring of the two signals shows a good correlation. The accuracy obtained on the slope (about one Airy disk ) let us be optimistic for the future full ELP-OA demonstrator with lasers. This work required an in-depth characterization of a detector featuring the novel EMCCD technology as well as the implementation and tests of pendular seismometers dedicated to measure telescope angular vibrations.
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Julien Girard. VALIDATION SUR LE CIEL DU CONCEPT D'ETOILE LASER POLYCHROMATIQUE. Astrophysique [astro-ph]. Université Claude Bernard - Lyon I, 2005. Français. ⟨tel-00106328v2⟩

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