  We numerically examine the spatial evolution of the structure of coherent and
partially coherent laser beams, including the optical vortices, propagating in
turbulent atmospheres. The influence of beam fragmentation and wandering
relative to the axis of propagation (z-axis) on the value of the scintillation
index (SI) of the signal at the detector is analyzed. These studies were
performed for different dimensions of the detector, distances of propagation,
and strengths of the atmospheric turbulence. Methods for significantly reducing
the scintillation index are described. These methods utilize averaging of the
signal at the detector over a set of partially coherent beams (PCBs). It is
demonstrated that the most effective approach is using a set of PCBs with
definite initial directions of propagation relative to the z-axis. This
approach results in a significant compensation of the beam wandering which in
many cases is the main contributor to the SI. A novel method is to generate the
PCBs by combining two laser beams - Gaussian and vortex beams, with different
frequencies (the difference between these two frequencies being significantly
smaller than the frequencies themselves). In this case, the effective
suppression of the SI does not require high-frequency modulators. This result
is important for achieving gigabit data-rates in long-distance laser
communication through turbulent atmospheres.
