Proceedings of 2015 Photonics & Electromagnetics Research Symposium, Prague, July 6 - 9,Page(s)2514-2516
Abstract
The scintillation index of focused higher order laser beam propagating in non-
Kolmogorov atmospheric turbulence is formulated by employing the Rytov method and the
equivalence of the structure constant. Our evaluations are performed for even modes. The
equivalence formula for the structure constant is extracted from our earlier work in which the
equivalence is obtained by equating the scintillation indices found in the Kolmogorov and the
non-Kolmogorov turbulence. If not specified otherwise, the focused beam is defined when the
focal length is equal to the link length. For the focused higher order laser beams, as the power law
exponent of the non-Kolmogorov spectrum decreases, the scintillations decrease. At any power
law exponent, the scintillations tend to become larger when the mode order of the focused beam
becomes larger, i.e., the focused Gaussian beam is advantageous over the focused higher order
laser beams for any realization of the non-Kolmogorov turbulence. Again being valid for any
power law exponent, increase in the source size is found to decrease the intensity fluctuations of
all the focused higher order mode scintillations. Especially for the larger order beams, focusing
the higher order beam at a distance smaller than the link length results in a change in the be-
haviour of the scintillation index versus the power law exponent. In such cases, the scintillations
are observed to increase. Comparison of the focused higher order beam scintillations with the
previously obtained collimated higher order beam scintillations yields that the focused higher or-
der beam scintillations are lower. Collimated higher order beams exhibit lower scintillations than
the collimated Gaussian beams whereas this is reversed in the focused case. Another observation
in such comparison shows that the difference of the intensity fluctuations between the Gaussian
and the higher order beams are much larger in the focused case, especially at larger power law
exponent values.
Citation
Yahya Kemal Baykal,
"Effects of Focusing on Scintillations of Higher Order Laser Modes in Non-Kolmogorov Turbulence," Proceedings of 2015 Photonics & Electromagnetics Research Symposium, Prague, July 6 - 9,Page(s)2514-2516