Hidden-phase compensation in extended-beacon adaptive optics

In this paper, we use wave-optics simulations to explore the benefits of hidden-phase compensation for laser systems that employ extended-beacon adaptive optics. Specifically, we create a trade space, where we vary the strength of the scintillation as well as the size of the beacon, and score laser-system performance in terms of no phase compensation, perfect least-squares compensation, and perfect full-phase compensation. Here, “full phase” refers to the least-squares and hidden-phase components of the pupil-plane phase function. The results of this trade space lead to three main conclusions. (1) If the scintillation is weak and we have either a point-source beacon or a very small extended-source beacon, then we see similar performance with perfect least-squares and full-phase compensation; however, both significantly improve performance compared to the no compensation case. On the other hand, if the scintillation is strong and we have either a point-source beacon or a very small extended-source beacon, then we get a significant improvement in performance using perfect full-phase compensation compared to perfect least-squares compensation. (2) If the scintillation is strong, then there will be a large number of turbulence-induced branch points and branch cuts in the hidden-phase component of the pupil-plane phase function. These branch points and cuts will result in a major reduction in performance if left uncompensated. (3) If the extended-source beacon is large, then the associated rough-surface scattering and resultant speckle will corrupt the perfect least-squares and full-phase compensation to the point where performance is on par with or worse than the no compensation case. At large, (1)–(3) will inform the development of future laser systems that need to mitigate the effects of scintillation and speckle to perform extended-beacon adaptive optics.