Spatial correlation of strong intensity fluctuations in a narrow laser beam traveling in the atmosphere

An experimental investigation was made of the spatial correlation function of strong fluctuations of the field intensity in a narrow collimated laser beam traveling in the atmosphere along an inclined path. It was found that, for given propagation conditions, the smallest scale of the intensity correlation in a beam differed considerably from the scale obtained in earlier experiments for unconfined plane and spherical waves. The correlation coefficient measured with a receiving aperture of variable diameter was the same as that measured with two point detectors and it agreed satisfactorily with the results of numerical calculations carried out using the generalized Huygens–Kirchhoff method.