Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Biomedical Engineering (PhD)

Administrative Home Department

Department of Biomedical Engineering

Advisor 1

Sean J Kirkpatrick

Committee Member 1

Jeremy Bos

Committee Member 2

Jeremy Goldman

Committee Member 3

Jingfeng Jiang

Abstract

Coherent light - such as that from a laser - on interaction with biological tissues, undergoes scattering. This scattered light undergoes interference and the resultant field has randomly added phases and amplitudes. This random interference pattern is known as speckles, and has been the subject of multiple applications, including imaging techniques. These speckle fields inherently contain optical vortices, or phase singularities. These are locations where the intensity (or amplitude) of the interference pattern is zero, and the phase is undefined.

In the research presented in this dissertation, dynamic speckle patterns were obtained through computer simulations as well as laboratory setups involving scattering from phantoms and animal tissues. Optical vortices were tracked within these patterns. Novel techniques were applied to relate scattering media dynamics with the temporal evolution of the speckle fields and the optical vortex locations. Parameters, such as optical vortex trail lengths, mobility of optical vortices and charge separation between different types of vortices were introduced and calculated. Mathematical formulations, namely Poincaré descriptors, were employed to analyze the statistics of speckle intensity and optical vortex dynamics.

A brief review of the advancements in the understanding and detection of optical vortices is presented. This is followed by the theory behind Poincaré analysis. It is concluded that Poincaré descriptors can be used to characterize the correlation in a data series. Speckle patterns with different dynamic behaviors – such as Brownian and Lorentzian modes of decorrelation between consecutive frames, at varying rates - were studied. It was noted that measuring the optical vortex parameters in a dynamically evolving field, provided insights into the decorrelation characteristics of the scattering medium. As speckle size is a statistical measure of the intensity variation in the field, the use of Poincaré descriptors to estimate speckle size is demonstrated. Additionally, these descriptors differentiate between short- and long-range orders in data. Laser speckle images obtained from flow in fluid phantoms and animal tissues indicated that Poincaré analysis provides an alternate method of quantifying flow.

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