This thesis describes a search for the rare radiative decay of a B meson to two photons. where the charged congugate mode is implied throughout. These decays are highly suppressed in the Standard Model where the branching fraction is expected to be of order 10^-8. In some new physics scenarios this could be enhanced by up to an order of magnitude to 10^-7. Therefore an observation of a significant signal above the Standard Model prediction could be a sign of new physics. The search for this rare decay was performed using the data collected with the BaBar detector at the SLAC National Accelerator Laboratory PEP-II storage ring operating at the Upsilon(4S) resonance. The analysis uses a dataset with an integrated luminosity of 425.7 fb-1 corresponding to 467 million BB pairs. A signal yield of 21.3 +12.8 -11.8 events with a significance of 1.88 sigma was measured using an unbinned extended maximum likelihood fit. An upper limit on the branching fraction is set at the 90% confidence level of less than 3.2 times 10^-7. This is about two times more stringent than the best upper limit of less than 6.2 times 10^-7 published by the Belle collaboration. / text

A new discrete ordinates method designed for use on modern, large memory, vector and/or parallel processing super computers has been developed. The method is similar to conventional SN techniques in that the medium is divided into spatial mesh cells and that discrete directions are used. However, in place of an approximate differencing scheme, a nearly exact matrix representation of the streaming operator is determined. Although extremely large, this matrix can be stored on today's computers for repeated use in the source iteration. Since the source iteration is cast in matrix form it benefits enormously from vector and/or parallel processing, if available. Several test results are presented demonstrating the reduction in numerical diffusion and elimination of ray effects.

Slow photon, or light with reduced group velocity, is a unique phenomenon found in photonic crystals that theoreticians have long suggested to be invaluable for increasing the efficiency of light-driven processes. This thesis demonstrates experimentally the feasibility of using slow photons to optically amplify photochemistry of both organic and inorganic systems. The effect of photonic properties on organic photochemistry was investigated by tracing out the wavelength-dependent rate of photoisomerization of azobenzene anchored on silica opals. The application of slow photons to inorganic photochemical processes was realized by molding nanocrystalline titania into an inverse opal structure and investigating its photodegradation efficiency in relation to the photonic properties. Changes in the photodegradation efficiency were directly linked to modifications of the electronic band gap absorption as a result of the photonic properties. The highest enhancement of twofold was achieved when the energy of the slow photons overlaps with the electronic band gap absorption, such that the loss of light due to photonic stop-band reflection was significantly reduced. In addition, the strength of slow-photon amplification with respect to the macroscopic structural order was studied by introducing controlled disorder via the incorporation of guest spheres into the opal templates. For the first time, a correlation between structural order, photonic properties and a photochemical process was established. The ability to combine slow-photon optical amplification with chemical enhancement was further achieved by incorporating platinum nanoparticles in inverse titania opals where the platinum nanoparticles increased the lifetimes of the higher population of electron-hole pairs arising from slow photon. Overall, various important factors governing the slow photon enhancement were investigated in detail, including the energy of the photonic stop band, angle dependence, thickness of the film, degree of structural order, filling fraction of the dielectric material and diffusion of a second medium if present. Theoretical calculations based on scalar-wave approximation in support of the experimental findings were provided wherever possible. The findings provide a blueprint for achieving optical amplification using slow photons in the broad range of photochemical or photophysical processes.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 24 May 2014. / The Sunyaev-Zel'dovich e ect (hereafter SZE), i.e. the distortion of the cosmic microwave background (CMB) spectrum due to inverse Compton scattering of CMB photons o energetic electrons in cosmic structures, is a relevant inves- tigation tool for astrophysical and cosmological studies. Since the SZE is an interaction between photons and electrons, polarization arises as a natural out- come and then provides the SZE with an important complementary component as an astrophysical and cosmological probe. This thesis is an extensive study on the SZE in non-relativistic and relativistic regime including polarization. We rst perform a study on a set of galaxy clusters hosting radio halos where we constrain the non-thermal pressure present in these structures using multifre- quency data such as SZE, radio and X-ray. We found that the average ratio between non-thermal to thermal pressure is 0:5. We then derive, in the full relativistic regime, a general formulation of the properties of the SZE, and we further derive the Stokes parameters, Q and U, of the polarized SZE. This is done in a general case by solving the polarized Boltzmann collisional integral in the Thomson limit that allows us to extract the Stokes parameters for arbitrary electron distribution functions. We further discuss the spectral features of the SZE polarization as produced by other additional e ects occurring in the clus- ter atmospheres, like nite optical depth e ects and transverse plasma motions. We nally apply the results of our study to di erent cosmic structures (e.g. galaxy clusters and radio galaxies) and we discuss the relevance of SZE polar- ization in the study of extragalactic astrophysical plasmas and for cosmological applications.

The angular momentum of light originates from two sources: one is the spin angular momentum (SAM) of individual photons, which is related to the polarization of light and the other is the orbital angular momentum (OAM) associated with helical wavefront of the light if it is helically phased (complex phase front). A beam of light that is composed of photons possessing both OAM and SAM states can be used in different areas of study such as rotating microscopic particles, interacting with nonlinear materials, investigating atom-light interactions, communication and medical imaging technologies, quantum information, quantum entanglement and etc. In this dissertation we study coherent beams that convey photons in superposition states of polarization and complex phase front. Our study includes two fields: (I) classical wave-like behavior with visible light in the field of singular optics. (II) quantum particle-like behavior of photons of light in the field of quantum-entangled optics. The approach is to investigate the state of such photons both mathematically and experimentally in classical-singular and quantum-entangled fields. We discuss seven projects based on this research. In one project we present a new method to encode OAM modes into perpendicular polarization components and making superpositions of polarization and spatial modes mapped by Poincare sphere. In another project using spatial light modulators (SLM) we realized highorder disclination patterns in the polarization map of the cross section of the beam. We also realize new forms of polarization disclination patterns (line patterns where rotational invariance is violated) known as monstars that were not previously seen. We proposed a new definition for characterizing these patterns since they can have zero or negative singularity index. In another project, instead of SLM we used q-plates to generate new forms of monstars. We proposed a robust and easy method for determining the topological charge of a complex phase front beam by inspecting the interference pattern the beam reflected from a wedged optical flat. In another project we encoded OAM modes onto orthogonal polarization components of a photon from an entangled pair and investigated the quantum entanglement. We also prepared a polarization entangled state and calculated some measures of entanglement. We summarize the projects and discuss the future prospects. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

In 2017, 98 gigawatts of solar capacity were added globally, outpacing new contributions from coal, gas and nuclear plants combined, based on 161 billion dollars of investment. Solar is the leading contributor to the clean energy revolution and continues to grow in market share and drop in price every year as economy of scale advances the technology. Within this market, silicon and cadmium telluride solar cells dominate nearly all of market share, converting roughly 20% of incident solar power into electricity. It is worth noting that the gains from a 1% increase in power conversion efficiency of the typical 20% solar cell to 21% would be measured, annually, in billions of dollars. If the solar cells installed last year had 1% more power conversion efficiency and the power displaced coal power generation, this enhancement in efficiency would now save roughly 8,000,000 pounds of carbon dioxide emission per hour every hour for the ~220,000-hour (~25 year) lifetime of the solar cells. Within this context, enhancing the power conversion efficiency of solar cells is crucial economically and environmentally. Because sunlight is incident on the earth as a broad spectrum of different colors, the energy of the photons spans a wide range. Unfortunately, the spectral range limits power conversion efficiency. For example, solar cells are transparent to photons with insufficient energy, while photons with excess energy relax to the band edge of the solar material, losing the excess energy as heat. This thesis focuses on improving the utilization of high energy photons currently lost to this thermalization process. In Chapter 1, we introduce the photophysical process of singlet exciton fission and give an overview of the field, with a focus on its potential for incorporation into photovoltaic devices. In Chapter 2-8, we discuss our results realizing singlet exciton fission in molecular systems, specifically bipentacenes. This chapter includes the synthesis of these materials, theoretical calculations predicting and rationalizing their photophysical behavior, and the spectroscopic characterization used to demonstrate the singlet fission process. In Chapter 3, we detail a modular synthetic approach to oligomers and even the first polymer of pentacene. We also discuss some basic properties of these materials using techniques such as linear absorption, cyclic voltammetry, and grazing incidence wide angle X-ray scattering spectroscopy. In Chapter 4, we investigate the photophysics of these materials. Photoluminescence upconversion spectroscopy reveals the decay of the singlet exciton on ultrafast timescales, while transient absorption spectroscopy is used to assign the singlet fission timescale, as well as to characterize the triplet absorption spectra. Chapter 5 discusses the synthesis and photophysics of homoconjugated and non-conjugated pentacene dimers, where singlet fission occurs through sigma bonds. Again, transient absorption spectroscopy is crucial to the assignment of the photophysics at play, but continuous wave time resolved electron spin resonance measurements yield additional insights into interaction between the resulting triplet pair excitons. Chapter 6 provides further detail into the formation of strongly exchange coupled triplet pair states. Continuous wave time resolved electron spin resonance spectroscopy is used to determine the quintet character of these states, and pulsed electron spin resonance measurements nutate the spin of these states to confirm this assignment. Chapter 7 provides the first demonstration that singlet exciton fission is also possible in heterodimer systems. Finally, Chapter 8 delves more deeply into the exciton correlations in these materials with a special focus on the pentacene-tetracene dimer system.

Ph.D. / Applied Physics & Electronic Science / Direct detection, photon counting receivers for use in optical communication through the clear air, turbulent atmosphere have been examined. In particular, spatial diversity arrays to overcome the effect off adding due to atmospheric turbulence are considered. Experimental results are compared with theoretical results for an optimum receiver structure based upon Bayes criterion of minimum probability of error. In addition, certain suboptimum receivers with simpler structures are derived directly from the optimum receiver. These receivers, along with an adaptive threshold receiver, are considered in order to examine the trade off between performance and complexity. The results indicate that the adaptive threshold receiver is a good compromise for information rates that are high with respect to scintillation frequencies, a relatively unrestrictive condition.

This dissertation presents a search for heavy, long-lived, neutral particles that decay to photons in proton anti-proton collisions with a center of mass energy of 1.96 TeV at the Collider Detector at Fermilab (CDF) experiment. Such particles are typical of models of Gauge Mediated Supersymmetry Breaking (GMSB). We select events with a single photon, missing transverse energy, and little other activity in the detector. We model the photon arrival time for Standard Model and non-collision sources using a data-driven method and consider photons which have a time of arrival at the detector which is significantly delayed relative to predictions. Using 6.3 fb^−1 of data collected from December 2004 to June 2010, we observe 322 events in the signal region compared to a background prediction of 287 ± 24 events. While the data are consistently above predictions, we report a model excess with a significance of 1.2 standard deviations from the null hypothesis.

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