Comparison of analytical and numerical estimations of laser beam spreading in a turbulent atmosphere

Two possible methods to solve scalar parabolic wave equation describing beam propagation in a randomly inhomogeneous medium have been compared in the article. The analytical approach was based on additive approximation, while numerically the equation was solved by the split-step Fourier algorithm. As was shown calculation of the beam radius with the use of both methods provides approximately the same results in the interval of weak fluctuations of the index of refraction. Increase of distortion intensity leads to divergence of data obtained analytically and in computer simulations. This disagreement can be explained by intrinsic limitations of additive approximation evolving in the regime of strong amplitude-phase fluctuations.