Mode Conversion of Gaussian Light Beams Propagating Through a Random Medium

Mode conversion of a Gaussian beam due to random fluctuations of a turbulent medium is discussed. The mean-square value of the mode-conversion coefficient (i.e., the power occupation of the higher mode in the perturbed field) is obtained by the perturbation technique. The results show that mode conversion decreases in the neighborhood of the focal point of a focused beam and that the decrease at that point becomes significant when the aperture size is large compared with the scale of the turbulence of the medium. The influence of the anisotropy of the fluctuations on mode conversion is also discussed.