Phase estimation for large field of view: application to multiconjugate adaptive optics

We propose a "Maximum A Posteriori-based" estimation of the turbulent phase in a large field of view (FOV) to overcome the anisoplanatism limitation in adaptive optics. We show that, whatever the true atmospheric profile, a small number of equivalent layers (2 or 3) is required to obtain an accurate restitution of the phase in the whole FOV. The implications on multiconjugate adaptive optics are discussed in terms of number and conjugated heights of the deformable mirrors. The number of guide stars for the wavefront measurements in the field is also discussed: 3 (or even 2) guide stars are sufficient to obtain good performance.