Title

Analysis of atmospheric turbulence effects on laser beam propagation using multi-wavelength laser beacons

Date of Award

2011

Degree Name

M.S. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Advisor: Mikhail A. Vorontsov

Abstract

Atmospheric turbulence affects optical systems that operate in various atmospheric conditions. The characteristics of the optical wave transmitted through atmospheric turbulence can undergo dramatic changes resulting in potential system performance degradation. Knowledge of atmospheric turbulence effects would aid in the development of a wide class of atmospheric-optics systems including laser communication, directed energy, lidar, remote sensing, and active and passive imaging systems. In the classical atmospheric turbulence theory, the refractive index structure parameter is the key parameter known to describe the strength of the atmospheric turbulence and accurate measurement of this parameter represents an important task. The refractive index structure parameter can be difficult to measure, as it is influenced by many factors including path length, time of day, season, and microclimate conditions which cannot be applied universally and may change in a matter of minutes. To further complicate atmospheric turbulence characterization, the key assumptions of classical (Kolmogorov) turbulence theory, such as statistical homogeneity and isotropy of the refractive index random field, are not always satisfied. From this viewpoint, experimental analyses to determine the applicability of the Kolmogorov turbulence theory in different optical wave propagation conditions represent important tasks and can assist in the adequate evaluation of atmospheric turbulence effects on optical system performance and design. In this thesis, the applicability of the classical turbulence theory was verified through simultaneous intensity measurements (pupil- and focal-plane intensity distributions) from multi-wavelength laser beacons over a near-ground, near-horizontal, and seven-kilometer-long propagation path. These measurements allowed independent evaluation of the refractive index structure parameter for two different wavelengths (λ1 = 532 nm, λ2 = 1064 nm), and these results were compared to theoretical predictions. In addition, the turbulence-induced intensity scintillations were investigated across the projected laser beam footprint, and a numerical analysis of the propagation was compared to the experimental data. To obtain the intensity measurements, the optical setup included four sub-systems using fast-framing (̃150 frames/second) cameras that were synchronized using previously developed control software; additional software was developed for data acquisition and processing. The conducted experiments in the turbulence conditions investigated here showed that the results of measurements and predictions based on the Kolmogorov turbulence theory are in reasonably good agreement but are particularly sensitive to the footprint position of the transmitted beacon. The atmospheric characterization technique using a multi-wavelength beacon provided a useful tool for examining the applicability of the Kolmogorov turbulence theory along this propagation path.

Keywords

Laser beams Atmospheric effects, Atmospheric turbulence Research, Meteorological optics Research

Rights Statement

Copyright 2011, author

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