The problem of light scattering in folded-path or double-passage configurations is studied theoretically. Assuming as the random medium a deep phase screen that introduces Gaussian-distributed phase fluctuations, we study the motion of the speckle as the source is moved. Some attention is also given to the phenomenon of backscattering enhancement. Our analysis is based on a novel expression for the complex amplitude that has a simple physical interpretation. For simplicity, only the one-dimensional case is considered, but an extension of the analysis to two-dimensional screens is not difficult.
Using the factorization properties of the moments of a complex Gaussian process, we are able to derive analytical expressions for the mean intensity and the intensity correlation of the backscattered radiation. We find that, in most cases, the speckle field decorrelates rapidly as one moves the angle of incidence and shifts toward the direction of specular reflection with a rate of motion that is different from that of the angle of incidence. We also find conditions under which, when the angle of incidence is modified, the speckle pattern produced in the region of observation tracks the backscattering direction.
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