Proceedings Article | 13 February 2009
KEYWORDS: Scintillation, Gaussian beams, Atmospheric propagation, Beam propagation method, Laser beam propagation, Atmospheric optics, Turbulence, Receivers, Atmospheric scintillation, Monochromatic aberrations
When different incidences are launched in atmospheric turbulence, it is known that the intensity fluctuations exhibit
different characteristics. In this paper we review our work done in the evaluations of the scintillation index of general
beam types when such optical beams propagate in horizontal atmospheric links in the weak fluctuations regime.
Variation of scintillation indices versus the source and medium parameters are examined for flat-topped-Gaussian, cosh-
Gaussian, cos-Gaussian, annular, elliptical Gaussian, circular (i.e., stigmatic) and elliptical (i.e., astigmatic) dark hollow,
lowest order Bessel-Gaussian and laser array beams. For flat-topped-Gaussian beam, scintillation is larger than the single
Gaussian beam scintillation, when the source sizes are much less than the Fresnel zone but becomes smaller for source
sizes much larger than the Fresnel zone. Cosh-Gaussian beam has lower on-axis scintillations at smaller source sizes and
longer propagation distances as compared to Gaussian beams where focusing imposes more reduction on the cosh-
Gaussian beam scintillations than that of the Gaussian beam. Intensity fluctuations of a cos-Gaussian beam show
favorable behaviour against a Gaussian beam at lower propagation lengths. At longer propagation lengths, annular beam
becomes advantageous. In focused cases, the scintillation index of annular beam is lower than the scintillation index of
Gaussian and cos-Gaussian beams starting at earlier propagation distances. Cos-Gaussian beams are advantages at
relatively large source sizes while the reverse is valid for annular beams. Scintillations of a stigmatic or astigmatic dark
hollow beam can be smaller when compared to stigmatic or astigmatic Gaussian, annular and flat-topped beams under
conditions that are closely related to the beam parameters. Intensity fluctuation of an elliptical Gaussian beam can also
be smaller than a circular Gaussian beam depending on the propagation length and the ratio of the beam waist size along
the long axis to that along the short axis (i.e., astigmatism). Comparing against the fundamental Gaussian beam on equal
source size and equal power basis, it is observed that the scintillation index of the lowest order Bessel-Gaussian beam is
lower at large source sizes and large width parameters. However, for excessively large width parameters and beyond
certain propagation lengths, the advantage of the lowest order Bessel-Gaussian beam seems to be lost. Compared to
Gaussian beam, laser array beam exhibits less scintillations at long propagation ranges and at some midrange radial
displacement parameters. When compared among themselves, laser array beams tend to have reduced scintillations for
larger number of beamlets, longer wavelengths, midrange radial displacement parameters, intermediate Gaussian source
sizes, larger inner scales and smaller outer scales of turbulence. The number of beamlets used does not seem to be so
effective in this improvement of the scintillations.
