Adaptive optical system referencing in the case of resolved targets illuminated through turbulence

The conventional feedback of multidither outgoing-wave adaptive optical systems is inoperative in the presence of a featureless target resolved by the transmitter optics. We propose in this paper to define an artificial glint by imaging the target laser pattern on a pinhole aperture. The concept is somewhat obvious, but in turbulence the existing theory on resolution and coherence states that it is restricted to small scintillation strength. Through correlation measurements between the physical-glint return and the artificial-glint irradiance, it is shown that the range of validity is much broader than predicted. Furthermore, tests with a two-degree-of-freedom system operated in turbulence demonstrate that the artificial-glint technique allows effective convergence at propagation distances reaching far into the scintillation-saturation region, i.e., well beyond the theoretical limit.