  We study propagation of two lowest order Gaussian laser beams with different
wavelengths in weak atmospheric turbulence. Using the Rytov approximation and
assuming a slow detector we calculate the longitudinal and radial components of
the scintillation index for a typical free space laser communication setup. We
find the optimal configuration of the two laser beams with respect to the
longitudinal scintillation index. We show that the value of the longitudinal
scintillation for the optimal two-beam configuration is smaller by more than
50% compared with the value for a single lowest order Gaussian beam with the
same total power. Furthermore, the radial scintillation for the optimal
two-beam system is smaller by 35%-40% compared with the radial scintillation in
the single beam case. Further insight into the reduction of intensity
fluctuations is gained by analyzing the self- and cross-intensity contributions
to the scintillation index.
