Consideration of atmospheric turbulence in laser systems design

The physical basis for various effects of atmospheric turbulence on laser systems is briefly discussed, and certain limitations of the theoretical results given by Tatarski are summarized. The most important conclusion is that Tatarski's results for amplitude and phase fluctuations, while they are not applicable for a laser beam of arbitrary diameter, do provide an adequate approximation when the beam diameter is at least a factor of 2 greater than the lateral correlation length for amplitude fluctuations, which is true in many applications. The effects analyzed in some detail are beam steering, beam spreading, image dancing, image blurring, scintillation, and phase fluctuations, certain of which are intimately related. As to specific applications, the signal-to-noise ratio for an AM signal passing through the turbulent atmosphere is derived in terms of the power fluctuation, and communication links are considered in terms of this ratio; the effect of power fluctuations on the probability of detection for the laser radar is discussed in general, and a special example is given; finally, the spot size on the moon's surface for a transmitter located on the earth's surface is calculated for different turbulence conditions.