Design of the extreme AO system for SPHERE, the planet finder instrument of the VLT

Abstract

The SPHERE system aims at the detection of extremely faint sources (giant extra-solar planet) in the vinicity of bright stars. Such a challenging goal automatically requires the use of a coronagraphic device to cancel out the flux coming from the star and smart imaging technics which have to be added to reach the required contrast for exo-planet detection (typically 10^-6 - 10^-7 in contrast). In this frame of the SPHERE project a global system study has demonstrated the feasibility of an AO system for the direct exoplanets detection. A detailed description of this system is proposed in this paper. The main trade-offs are discussed and justified and all the subsystems briefly presented. The realization phase has begun in 2006 and we foresee to obtain a first light at the VLT in 2010.