Mitigating Tilt Anisoplanatism with the Slope Merging Method for Multi-Conjugate Adaptive Optics Systems

Large optical telescopes depend on adaptive optics for the real-time compensation of turbulence-induced wavefront aberrations. The performance of laser guide star based Multi-Conjugate Adaptive Optics systems is degraded by tilt anisoplanatism. In this paper we propose and derive a method for mitigating this effect, achieved by merging the measurements of natural and laser guide stars together. This method performs a modal reconstruction of the field dependent Tip-Tilt aberration that is not sensed by the high order laser guide stars. The proposed method benefits from its (i) reduced computational load, (ii) compatibility with predictive control schemes, and (iii) improved uniformity of image quality over the whole science field of view. End-to-end numerical simulations are used to demonstrate the performance of the slope merging method in modern Adaptive Optics systems.