Laser Tomographic AO system for an Integral Field Spectrograph on the E-ELT : the ATLAS project
T. Fusco(1), S. Meimon(1), N. Thatte(2), H. Schnetler(3), Y. Clenet(4),M. Cohen(5), J. Paufique(6), P. Ammans(5), F. Clarke(2), J.-L. Dournaux(5), M. Ferrari(7), D. Gratadour(4), N. Hubin(6), P. Jagourel(5), V. Michau(1), C. Petit(1), M. Tecza(2)
(1) ONERA (2) Oxford Univ. (3) UK-ATC (4) Observatoire de Paris – GEPI (5) Observatoire de Paris – LESIA (6) ESO (7) Observatoire de Marseille – LAM
ATLAS (Advanced Tomography with Laser for AO system) is the LTAO module of the E-ELT. It should be combined with an Integral Field Spectrograph (HARMONI). It aims at providing a diffraction limited PSF (SR around 50% in K band) in a small scientific FoV for a very significant part of the sky (more than 60% of the whole sky). 6 Laser Guide Stars (located on a 4.3 arcmin ring) will be used together with 2 Natural Guide Stars to be picked off in a 2 arcmin FoV. A MMSE-based RTC algorithm will be considered to obtain an optimal tomographic reconstruction of the turbulent volume and correct for Laser defects (cone effects). A first concept of the module combined with opto-mechanical implementation and associated performance has been proposed in the frame of the E-ELT instrumentation phase A study. Further modifications and optimisations have been proposed to account for IFS-HARMONI specificities.
In this presentation, the main ATLAS components are described and their specificities and innovation highlighted. In particular, a new concept for the natural guide star wavefront sensor (based on a focal plane measurement scheme) is proposed providing extremely good sky coverage. In addition, the impact of Cn² mis-calibrations is analyzed and solutions to mitigate this error are proposed.
In addition, the specific HARMONI requirements are presented as well as their impacts on ATLAS design, calibration procedures and operational concept. An integrated approach for a common implementation of ATLAS-HARMONI is presented. Results show the feasibility of the concept, its versatility and a relative simplicity which is a good first step toward a potential implementation in the early years of the E-ELT.