Beacon-defined performance of adaptive optics

Achieving a minimal size laser spot (beacon) on a remote object is a major objective of the adaptive optics-based phase conjugations methods used in laser communications and directed energy systems. Achieving this goal not only requires a high quality conjugation of the laser beam wave front relative to the object-returned beacon beam, but also fulfillment of the reciprocity condition. The latter can be defined as precise matching of the intensities and wave fonts of two contrapropagating beams in each cross section along the propagation path. This condition is central for effectively focusing a laser beam on a remote object. Violation of the conditions of reciprocal propagation occurs, for example, when the receiving aperture is of limited size compared to the size of the object-returned beacon beam. Such size disparity between the receiving aperture and beacon returned beam results in decreased power density on the focused spot and reduced intensity of the target-returned beam. When the beacon wave is formed on a rough-surface object there is an additional decrease in the efficiency of the beam focusing. The paper provides a detailed discussion of these phenomena.