Experimental measurement of the fluctuations of a laser beam due to thermal turbulence.
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Date
2013
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Abstract
In this work, we considered and developed a new method to detect and quantify the
fluctuations of a laser beam due to thermal turbulence. The new method consisted
of a single laser beam propagating in air and passing through a point diffraction
interferometer (PDI). Stable interferograms were thus formed by diffraction of light at
the PDI pinhole. Such interferograms underwent phase shifts due to the application
of simulated thermal turbulence on the propagating laser beam. These phase shifts
were then used to obtain atmospheric turbulence parameters such as the atmospheric
turbulence strength, temperature near the propagating beam and the scintillation
index.
Chapter 1 of this thesis is an introduction and discussion of the theory on the
propagation of laser beams in air. Gaussian beam propagation, turbulence detectors,
Rytov’s theory and Kolmogorov’s theory of turbulence is also discussed in detail.
artefact descriptive experimental procedure is then provided. This chapter focuses
on the behavior of a laser beam propagating under the conditions of weak turbulence
and relates the Rytov weak fluctuations to the Kolmogorov spectrum since the Rytov
variance can be exactly equal to the scintillation index under the conditions of weak
turbulence.
Two unpublished scientific papers were submitted for publication to the Canadian
Journal of Physics and Europian Journal of Remote Sensing. Chapter 2 consist of
paper 1 which is based on the development of the experiment and it describes the
apparatus in detail as well as it explains the experimental procedure. The preliminary
results presented in paper 1 showed that a PDI can produce stable interferograms
that can be used to extract the atmospheric turbulence parameters and thus, the
PDI method can be used for atmospheric detection and ranging. In chapter 3, we
discussed and analysed the experimental results, where the phase shifts were used to
estimate the temperature that caused the purturbations on the interferograms. In
chapter 4, we concluded about the use of a PDI as a remote sensing technique.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
Keywords
Physics., Theses--Physics.