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Closed-loop with laser guide star spot elongation: impact of a maximum a posteriori reconstruction with modeled noise correlations on end-to-end simulations

Abstract 308

Submitted by Clémentine BÉCHET


C. Béchet (1), M. Le Louarn (1), R. Clare (1), M. Tallon (2), I. Tallon-Bosc (2), É. Thiébaut (2)


(1) European Southern Observatory, Karl-Schwarzschild-Strasse 2 , 85748 Garching, GERMANY; (2) Centre de Recherche Astrophysique de Lyon - Observatoire de Lyon, 9 Avenue Charles André 69561 Saint Genis Laval cedex, FRANCE


Laser guide stars (LGS) on an Extremely Large Telescope (ELT) produce elongated spots on the subapertures of the Shack-Hartmann wavefront sensors. This degrades the measurements accuracy and introduces structured correlations in the centroiding errors, depending on the position of the laser launch telescope with respect to the subapertures location inside the pupil. Advanced centroiding algorithms are used to maintain satisfying accuracy in the measurements, but closed-loop control methods in adaptive optics usually neglect the structured errors correlations. However, properly modeling the noise correlations is expected to improve the correction. We take into account the errors statistics inside a fast algorithm for wavefront reconstruction and control on a ELT-class telescope. The closed-loop performance of the new algorithm, including a maximum a posteriori reconstruction and an internal model control is studied. It is compared to the classical command matrix multiplication, neglecting the noise correlations, with an integrator control. End-to-end simulations are involved to compare the two approaches. Both a single-LGS and a multiple-LGS system are simulated. The latter allows to provide additional information to the discussion about the choice of laser launch telescope positions on an ELT-class telescope.

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