Branch-point compensation in extended-beacon adaptive optics

In this paper, we use wave-optics simulations to explore laser propagation system performance. We accomplish this by creating a trade space where we vary turbulence conditions as well as beacon size from a point-source beacon to an extended-source beacon with an object Fresnel number, N_obj, of 20. We explore performance when we employ no compensation, perfect phase compensation, and perfect full-phase compensation. The results of this trade space allow us to arrive at three main conclusions. First, if we have either a point-source beacon or a very small extended-source beacon and turbulence is strong, we get a significant improvement in performance using full-phase compensation compared to least-squares compensation and no compensation. If turbulence is weak, we see similar performance with least-squares and full-phase compensation, however, both are significantly improved over the no compensation case. Second, in strong turbulence conditions, there will be a very large number of turbulence-induced branch points. If left uncompensated, these turbulence-induced branch points will result in a major reduction in performance. Lastly, when the extended-source beacon is large, the associated rough-surface-scattering-induced phase aberrations will corrupt the compensation to the point where the drawbacks of compensating for surface-roughness-induced aberrations significantly outweigh the benefits of compensating for turbulence-induced aberrations. These results (1) inform researchers looking to conduct extended-source-beacon adaptive optics and (2) motivate research to explore methods for speckle mitigation in adaptive-optics systems.