Effect of turbulent fluctuations in an optically active fluid medium

Abstract

The effect of a beam traversing an optically active medium of turbulent fluctuations of the index of refraction in the medium is investigated theoretically. The general far-field case is solved by integration of the wave equation with both gain and fluctuations of the index refraction, simplified by neglecting the Laplacian of the fluctuating part of the electric field and one of the time derivatives. The far-field diffraction pattern is identical to that for a nonactive medium. For small to moderate extinction there is a loss of power from the coherent beam but only a slight change in the diffraction pattern, accompanied by wide-angle incoherent scattering. For high-gain cases it is possible to have the extinction coefficient less than the gain, but with complete extinction of the coherent beam and a large incoherent scattering pattern. The use of a more realistic turbulence spectrum than previously used has led to the discovery of a second branch in the resolution curve, in which the resolution far exceeds the previously given “limiting resolution” as the aperture size is increased beyond a certain limit, and approaches the diffraction pattern based on the aperture, although there may be considerable attenuation in the intensity in the diffraction pattern of the coherent beam. These results are applicable, for example, to the use of large aperture optics in turbulene wind tunnels. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.