Lee Wai Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 177-181). / List of Figures and Tables --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Photonic Band Gap materials --- p.1 / Chapter 1.2 --- Theoretical Calculation on PBG materials --- p.5 / Chapter 2 --- Plane Wave Expansion --- p.13 / Chapter 2.1 --- Plane Wave Expansion within Scalar Wave Approximation --- p.14 / Chapter 2.2 --- Plane Wave Expansion to Scalar I and II Equations --- p.21 / Chapter 3 --- Formalism of Photonic k.p Theory --- p.33 / Chapter 3.1 --- Vectorial k.p formulation --- p.33 / Chapter 3.2 --- Scalar k. p formulations --- p.36 / Chapter 4 --- Implementation and k.p Band Structures --- p.38 / Chapter 4.1 --- Evaluation of Integrals plj and qlj --- p.38 / Chapter 4.2 --- k.p Band Models --- p.47 / Chapter 5 --- Dependence of k .p Parameters on Dielectric Contrast and Fill- ing Ratio --- p.57 / Chapter 5.1 --- Accuracy of Integrals plj and qlj --- p.57 / Chapter 5.2 --- Sensitivity of k.p Parameters to System Parameters --- p.71 / Chapter 6 --- Empirical Tight-binding Scheme --- p.99 / Chapter 6.1 --- Electronic Tight Binding Approximation --- p.99 / Chapter 6.2 --- Empirical Tight-binding Scheme --- p.101 / Chapter 7 --- Summary --- p.137 / Chapter A --- Preprint of Ref. [36] --- p.144 / Chapter B --- The Coefficients in Eq. (2.22) --- p.161 / Chapter C --- Formalism of Photonic k.p Theory --- p.163 / Chapter D --- The Coefficients in Eq. (5.2) --- p.166 / Chapter E --- The Coefficients in Eq. (5.3) --- p.168 / Chapter F --- The Coefficients in Eq. (6.15) --- p.170

One of the daunting challenges in wave physics is to accurately control the flow of light at the subwavelength scale. By patterning the optical medium one can design anisotropic artificial medium, this engineering method is commonly known as photonic crystals or metamaterials. Negative or zero index of refraction, slow-light propagation, cloaking with transformation optics material, and beam collimation are only a few such unique functionalities that can be achieved in engineered media at the subwavelength scale. Another interesting phenomenon in wave physics, Anderson localization, which suggests electron localization inside a semiconductor, has been intensely investigated over the past years, including transverse localization in bulk and waveguide arrays periodic in one and two dimensions. Here we report the photon transport and collimation enhanced by transverse Anderson localization in chip-scale anisotropic artificial medium, a similar physical model to doping the impurity in insulator and turning it into a semiconductor. First, by engineering the photonic crystal, we demonstrate a new type of anisotropic artificial medium for diffraction-free transport through cascaded tunneling of guided resonances. High-resolution near-field measurements demonstrate the coupling of transverse guided resonances, supported by large-scale numerical modeling. Second, with the disordered scattering sites in this superlattices, we uncover the mechanism of disorder-induced transverse localization in chip-scale. Arrested spatial divergence is captured in the power-law scaling, along with the exponential asymmetric mode profiles and enhanced collimation bandwidth for increasing disorder, over 4,000 scattering sites. With increasing disorder, we observe the crossover from cascaded guided resonances into transverse localization regimes, beyond the ballistic and diffusive transport of photons. As disorder is ubiquitous in natural and artificial materials, the transport through random media is of great importance. It also leads to various interesting optical phenomena, of which the most surprising one is Anderson localization of light. However, not all the states in disordered system are localized. Nonlocalized modes that extend over the whole sample via coupling between multiple local cavities with similar resonance frequencies are also present in disordered systems. These extended modes are called necklace states. Here, we also show that long-distance beam collimation can be witnessed in millimeter-scale photonic crystals that were fabricated lithographically with ultrahigh resolutions. By precisely controlling the disorder level of three million scattering sites in photonic crystals, we uncovered the transformation of light flows from the propagation of regular Bloch modes to necklace states.

The analytical solution to a model time-dependent continuous lethargy photon transport equation is evaluated numerically to obtain a benchmark solution using the Laplace transforms coupled with the multiple collision expansion method. The benchmark solution is then used to check the accuracy of the multigroup approximation. Excellent agreement between continuous lethargy benchmarks and multigroup approximation is obtained.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 58-59). Also available in electronic version. Access restricted to campus users.

Thesis (M. S.)--Nuclear and Radiological Engineering and Medical Physics, Georgia Institute of Technology, 2010. / Committee Chair: Rahnema, Farzad; Committee Member: Wang, Chris; Committee Member: Zhang, Dingkang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The Coarse-Mesh Transport Method (COMET) is a method developed by the Computational Reactor and Medical Physics Group at Georgia Tech. Its original application was neutron transport for nuclear reactor modeling. COMET has since been shown to be effective for coupled photon-electron transport calculations where the goal is to determine the energy deposition of a photon beam. So far COMET can simulate a mono-directional, mono-energetic, spatially-flat photon beam. The goal of this thesis will be to extend COMET by adding a generalized source treatment. The new source will be able to simulate beams that vary in intensity as a function of position, angle, and energy. EGSnrc will be used to verify the accuracy of the new method for 3D photon kerma calculations.

Solutions were developed to solve the special photon transport problems. A respective Monte Carlo code were implemented. The photon transport calculations were made for simulation of light distribution in tissues, for 3D estimation of dosis brachytherapy source, for determination of scattering coincidences in PET and for solving of one special problem for ambient dosimetry. The developed calculation methods are based on a purely statistical approach and can therefore universal applied. The efficiency in respect of precision, numerical effectiveness, as well as memory requirement were optimised and verified by the calculations done. The modification and enhancement can be easy realised thanks to modular, object orientated implementation of the program and enables development of new application fields in physics and medicine. / Zur Lösung speziellen Probleme des Photonentransports wurden grundlegende Ansätze gewonnen und in einem Transportprogramm umgesetzt. Die Photonen-Transportrechnungen zur Simulation des Lichttransports in trüben Medien, für die dreidimensionale Dosisberechnung für interstitielle Brachytherapiequellen, für die Ermittlung der Streustrahlungsverteilungen in PET-Scannern und für die Lösung eines speziellen Problems der Umgebungsdosimetrie wurden durchgeführt. Die entwickelten Berechnungsmethoden basieren auf einer rein probabilistischen Herangehensweise und lassen sich deshalb universell verwenden. Ihre Leistungsfähigkeit hinsichtlich der Genauigkeit, der numerischen Effektivität sowie des Bedarfs an Rechenresourcen wurde optimiert und konnte durch die durchgeführten Berechnungen bestätigt werden. Durch den modularen, objektorientierten Programmaufbau sind Modifikationen und Erweiterungen relativ einfach durchzuführen. Das ermöglicht eine Erschließung von neuen Anwendungsgebieten in der Physik und Medizin.

Solutions were developed to solve the special photon transport problems. A respective Monte Carlo code were implemented. The photon transport calculations were made for simulation of light distribution in tissues, for 3D estimation of dosis brachytherapy source, for determination of scattering coincidences in PET and for solving of one special problem for ambient dosimetry. The developed calculation methods are based on a purely statistical approach and can therefore universal applied. The efficiency in respect of precision, numerical effectiveness, as well as memory requirement were optimised and verified by the calculations done. The modification and enhancement can be easy realised thanks to modular, object orientated implementation of the program and enables development of new application fields in physics and medicine. / Zur Lösung speziellen Probleme des Photonentransports wurden grundlegende Ansätze gewonnen und in einem Transportprogramm umgesetzt. Die Photonen-Transportrechnungen zur Simulation des Lichttransports in trüben Medien, für die dreidimensionale Dosisberechnung für interstitielle Brachytherapiequellen, für die Ermittlung der Streustrahlungsverteilungen in PET-Scannern und für die Lösung eines speziellen Problems der Umgebungsdosimetrie wurden durchgeführt. Die entwickelten Berechnungsmethoden basieren auf einer rein probabilistischen Herangehensweise und lassen sich deshalb universell verwenden. Ihre Leistungsfähigkeit hinsichtlich der Genauigkeit, der numerischen Effektivität sowie des Bedarfs an Rechenresourcen wurde optimiert und konnte durch die durchgeführten Berechnungen bestätigt werden. Durch den modularen, objektorientierten Programmaufbau sind Modifikationen und Erweiterungen relativ einfach durchzuführen. Das ermöglicht eine Erschließung von neuen Anwendungsgebieten in der Physik und Medizin.

Despite significant advances in medical imaging technologies, there currently exist no tools to effectively assist healthcare professionals during surgical procedures. In turn, procedures remain subjective and dependent on experience, resulting in avoidable failure and significant quality of care disparities across hospitals. Optical techniques are gaining popularity in clinical research because they are low cost, non-invasive, portable, and can retrieve both fluorescence and endogenous contrast information, providing physiological information relative to perfusion, oxygenation, metabolism, hydration, and sub-cellular content. Near-infrared (NIR) light is especially well suited for biological tissue and does not cause tissue damage from ionizing radiation or heat. My dissertation has been focused on developing rapid imaging techniques for mapping endogenous tissue constituents to aid surgical guidance. These techniques allow, for the first time, video-rate quantitative acquisition over a large field of view (> 100 cm2) in widefield and endoscopic implementations. The optical system analysis has been focused on the spatial-frequency domain for its ease of quantitative measurements over large fields of view and for its recent development in real-time acquisition, single snapshot of optical properties (SSOP) imaging. Using these methods, this dissertation provides novel improvements and implementations to SSOP, including both widefield and endoscopic instrumentations capable of video-rate acquisition of optical properties and sample surface profile maps. In turn, these measures generate profile-corrected maps of hemoglobin concentration that are highly beneficial for perfusion and overall tissue viability. Also utilizing optical property maps, a novel technique for quantitative fluorescence imaging was also demonstrated, showing large improvement over standard and ratiometric methods. To enable real-time feedback, rapid processing algorithms were designed using lookup tables that provide a 100x improvement in processing speed. Finally, these techniques were demonstrated in vivo to investigate their ability for early detection of tissue failure due to ischemia. Both pre-clinical studies show endogenous contrast imaging can provide early measures of future tissue viability. The goal of this work has been to provide the foundation for real-time imaging systems that provide tissue constituent quantification for tissue viability assessments. / 2018-01-09T00:00:00Z

A hypothetical smuggling of material suitable for a nuclear weapon is known as a threat scenario. There is a considerable effort by the U.S. government to reduce this threat by placing radiation detectors at key interdiction points around the world. These detectors provide deterrence and defense against smuggling attempts by scanning vehicles, ships, and pedestrians for threat objects. Formulating deployment strategies for these detectors within the global transportation network requires an understanding of the complex interactions between the attributes of a smuggler and the detection systems. These strategies are rooted in the continued development of novel detection systems and alarm algorithms. Radiation transport simulation provides a means for characterizing detection system response to threat scenarios. However, this task is computationally expensive with existing radiation transport codes. Furthermore, the degrees of freedom in smuggler and threat scenario attributes create a large, constantly evolving problem space. Previous research has demonstrated that decomposing the scenario into independently simulated components using Green's functions can simulate photon detector signals with coarse energy resolution. This dissertation presents a general form of this approach, applicable to a wide range of threat scenarios through physics enhancements and numerical treatments for high energy resolution photon transport, neutron transport, and time dependent transport. While each Green's function implicitly captures the full transport phase-space within each component, these new methods ensure that this information is preserved between components. As a result, detector signals produced from full forward transport simulations can be replicated within 20% while requiring multiple orders of magnitude less computation time. This capability is presented as a general threat scenario simulation platform which can efficiently model a large problem space while preserving the full radiation transport phase-space. / text