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Active Laser Guide Star refocusing system for EAGLE instrument

Abstract 109

Submitted by Emmanuel HUGOT


J.-G. Cuby, M. Ferrari , J.-L. Gimenez, E. Hugot , D. Le Mignant, F. Madec, S. Mazzanti, S. Vives, P. Vola


Laboratoire d’Astrophysique de Marseille


For LGS assisted AO systems, the distance from the LGS spot to the telescope pupil ranges from 80 to 200km, depending on the Sodium layer altitude and the elevation of the telescope. This variation leads to a defocusing effect on the LGS wave-front sensor which needs to be compensated. In the specific case of the EAGLE multi-object spectrograph, one of the E-ELT instruments, we propose a solution based on an original optical design including an active optics component. This design could also be applied to other system as for instance ATLAS, the Laser Tomography module for E-ELT. In this paper we present the EAGLE original optical design for the extraction and the refocusing of the LGS and the developments carried on for the active optics component. This LGS Variable Curvature Mirror (LGS-VCM) is a 200mm parabolic active mirror able to achieve a 800µm deflection sag allowing the radius of curvature variation corresponding to the required range. Results of FEA simulations, embedded metrology concept and similar mirror prototypes will be also presented.