23 September 1997 Damping of intensity fluctuations for laser beams propagating in snowfalls
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Abstract
Intensity fluctuations of laser beams propagating through precipitation reveal the regularities that are different from those for the turbulent atmosphere. Specifically, three regimes of fluctuations can be observed. The first one is the weak scintillation regime where the scintillation index increases with the propagation path. The second regime is the fluctuation saturation where the scintillation index approaches a constant. This saturation level can be an arbitrary number unlike the turbulent atmosphere. The further increase of the propagation path leads to damping of intensity fluctuations. This regime has no analogy in the case of the turbulent atmosphere. In the proposed paper, the regime of fluctuation damping in snowfalls is studied both experimentally and theoretically. The experimental setup consists of a narrow laser beam propagating through a 2 km path. A small detector of 0.1 mm of diameter was placed on the optical axis. The dependence of scintillation index on the optical depth of the path and of flowsnake sizes were considered. According to the fluctuation model proposed early by the authors, the scintillation index can be calculated theoretically by means of numerical solution of the radiative transfer equation. The equation is solved by the Monte-Carlo code with some model phase function for a snowflake. The damping factor of scintillations is calculated as a function of the optical depth and of the angular divergence of the laser beam. Comparison of the calculated and experimental data is presented.
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Anatoli G. Borovoi, Boris A. Kargin, Sergei M. Prigarin, Nikolai A. Vostretsov, Anatoly F. Zhukov, "Damping of intensity fluctuations for laser beams propagating in snowfalls", Proc. SPIE 3125, Propagation and Imaging through the Atmosphere, (23 September 1997); doi: 10.1117/12.283891; https://doi.org/10.1117/12.283891
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