Fundamental considerations for wavefront sensing with extended random beacons

Extending adaptive optics to laser beam control over long turbulent paths where there is no cooperative beacon present requires examination of wave front sensor performance in new regimes. In some scenarios of interest it is necessary to create beacon by sending an illuminator laser through the atmosphere to scatter from the target, which, in general, must be considered to be optically rough. Scattered light returned to the laser transmitter aperture is referred to as the beacon field, and this light may be used for wave front sensing. Physical effects on the beacon field which reduce wave front sensing accuracy include turbulence induced beam broadening and speckle on the outgoing beam, and coherent laser speckle effects in the scattered field. In this paper we analyze the impact of these phenomena on some of the measurements available for tracking and wave front sensing.