Modelling wave transport in random media for wavefront shaping applications
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Full Text E-thesis
Date
2022
Authors
Raju, Michael
Journal Title
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Volume Title
Publisher
University College Cork
Published Version
Abstract
The central theme of my thesis is to develop various analytical and
numerical methods, for the coherent control of waves to assist various
wavefront shaping applications in random disordered media. This resulted in the development of 2D scalar wave transport modelling frameworks, analytically and computationally, from the scratch. The modelling
frameworks cover both frequency domain and time domain. In the frequency domain, the generalised scattering matrix (S matrix) incorporating evanescent modes is used to the study the transport properties. The
wavefront shaping methods in the frequency domain involve eigenchannels
and iterative phase conjugation for the enhancement of total transmission
through slab disorders and disordered constrictions. The generalisation
of the conventional Fisher-Lee relations to incorporate evanescent modes
is presented in the thesis. S matrices of spatially correlated disorders
are estimated using the generalised Fisher-Lee relations, incorporating
the Green’s function perturbation method. The comparison between the
conventional diffusion theory and the wave transport theory is presented,
which involves the cascading of S matrices and the transmission scaling law. The relationship between the spatial correlation of the disorder
and various transport properties are also investigated in this comparison. In the time domain, using the finite difference time domain scheme,
wavefront shaping involving iterative phase conjugation onto a space-time
modulated (STM) guide-star region operating in the Raman-Nath regime,
is investigated. The intention of studying the STM is to investigate the
potential of the acousto-optic effect for imaging through random media.
In the time domain, the effect of sample decorrelation due to Brownian
motion on the stability of the focussing is also studied using the Langevin
equation. The discussion of the analytical and numerical aspects of the
developed models, along with the availability of simulation codes written
in Matlab, may be of interest to wavefront shaping researchers interested
in characterisation of various wave transport behaviours.
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Keywords
Wavefront shaping , Wave transport theory and modelling , Random media
Citation
Raju, M. 2022. Modelling wave transport in random media for wavefront shaping applications. PhD Thesis, University College Cork.