Intensity fluctuations of focused laser beam during reflection in turbulent atmosphere

The relative dispersion of intensity fluctuations in a reflected focused laser beam are investigated experimentally as a function of the diffraction parameter of a transmitter, the type of reflector and the intensity of the turbulence along the propagation path. The measurements were made on a uniform horizontal path 300 m long with simultaneous optical measurements of the structural characteristic of the fluctuations in the index of refraction of the air. It is found that the dispersion of the intensity fluctuations in a narrow beam exceeds the corresponding quantity in a wider beam, as is the case for a collimated beam. The saturation level of the relative dispersion of the intensity fluctuations of the reflected focused beam is closed to the saturation level of relative dispersion in a spherical wave. This is apparently because a spherical wave reaches the receiver after the focused beam is reflected. The direct and reflected waves cover the entire distance from the transmitter to the receiver without passing through correlated atmospheric irregularities. The relative dispersion of the intensity fluctuations of a reflected focused laser beam is found to depend upon the diffraction parameter of the radiating aperture, as well as the type of reflector, as in the case for a collimate beam.