Quantitative optical phase imaging techniques, such as optical diffraction tomography (ODT), are useful tools for refractive-index profiling. Many of them, however, rely on the weak-scattering assumptions, thus cannot be applied to multiple-scattering objects, or turbid media. In this thesis, I report several approaches for expanding the efficacy of ODT techniques and adapting them to new applications by use of low-coherence broadband illumination. First, I developed a method for ODT reconstruction using regularized convex optimization with a new phase-based fidelity criterion. The new criterion is necessary because objects with very different refractive-index distributions may produce similar diffracted fields (magnitude and principal-phase) on the detection planes. This surjective, but non-injective relation, attributed to the cyclical nature of the phase, makes optimization algorithms using a field-based cost function prone to local minima, particularly for objects introducing large optical pathlength difference. I developed a phase-based optimization algorithm that avoids this and successfully tested it using simulations on phantoms and experimental data measured from samples of optical fibers. I have developed a method that applies total-variation regularization at each iteration of an iterative framework for ODT, which was developed with co-workers. I performed numerical and experimental tests using various highly scattering objects and demonstrated significant improvement in reconstruction SNR. I have also designed and constructed a new experimental setup for ODT measurement and expanded the new ODT algorithms from 2D to 3D. These algorithms have been numerically and experimentally validated using simulated data and data collected from the new experimental setup. Additionally, I have investigated the use of temporally incoherent illumination in ODT and showed that it enables time-gating of artifacts caused by multiple-scattering. I have further demonstrated that ODT combined with Fourier-transform spectroscopy can be used for spectral tomographic imaging of the wavelength-dependent complex-valued refractive index volumetric distributions.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Smith-Dryden, Seth, "Optimization-Based Approaches to Low-Coherence Optical Diffraction Tomography" (2022). Electronic Theses and Dissertations, 2020-. 1293.