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The scintillation index is evaluated in horizontal turbulent atmospheric optical links for incidences of incoherent cosh-Gaussian (IChG), cos-Gaussian (ICG) and annular (IA) beams. Weak turbulence solution is obtained for a slow detector.
Dependence of the intensity fluctuations of the IChG, ICG and IA beams on the link length, source size, wavelength and
the structure constant are examined. At all the link lengths, fixed size IChG and ICG beams exhibit lower scintillations
for larger absolute displacement parameters. At a fixed link length, IChG beam yields lower fluctuations than the ICG
beam having the same absolute displacement parameter. For the same size primary beams, IA beam with narrower ring
scintillates less than the IA beam with wider ring, and this holds to be valid for each link length. Investigation of the
scintillation versus the source size reveals that increase in the source size lowers the scintillations for all types of the
incoherent beams. At the same source size and the same absolute displacement parameter, IChG beams have lower
fluctuations than the ICG beams, larger absolute displacement parameters exhibiting lower scintillations at the same
source size for both beams. For IA beams, as the size of the primary beam is increased, the scintillations are reduced for
all ring sizes, the reduction being pronounced for narrower rings. As the wavelength increases, the scintillations of IChG
and ICG beams first increase, then at around the wavelength forming the Fresnel zone, the scintillations start to decrease
and eventually for all types of IChG and ICG beams, the scintillation indices merge towards a certain value. Similar
behaviour of the scintillations versus the wavelength is observed for IA beams as well. As long as the structure constant
is kept within the range of interest to remain in the weak turbulence, raising the structure constant first increases the
intensity fluctuations of beams for all the mentioned beam types where further rises in the structure constant result in the
same level of scintillation index. Comparison of the scintillations of IChG, ICG and IA beams with their coherent
counterparts and the coherent Gaussian beam shows that the IChG, ICG and IA beams are favorable for large sized
sources.
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