The scintillation index is formulated for a flat-topped Gaussian beam source in atmospheric
turbulence. The variations of the on-axis scintillations at the receiver plane are evaluated versus the
link length, the size of the flat-topped Gaussian source, and the wavelength at selected flatness
scales. The existing source model that represents the flat-topped Gaussian source as the
superposition of Gaussian beams is employed. In the limiting case our solution correctly
matches with the known Gaussian beam scintillation index. Our results show that for flat-topped
Gaussian beams scintillation is larger than that of the single Gaussian beam scintillation when
the source sizes are much smaller than the Fresnel zone. However, this trend is reversed and
scintillations become smaller than the Gaussian beam scintillations for flat-topped sources
with sizes much larger than the Fresnel zone.
© 2006 Optical Society of America
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