Theses/Dissertations - Physics
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Item Advanced light manipulation and waveguiding in plasmonic nanostructured optical fibers.(2021-04-29) Ghimire, Indra Mani, 1985-; Lee, Ho Wai (Howard); Zhang, Zhenrong.Conventional optical fibers are well-known for their efficient light guiding mechanism. However, the dielectric properties of core and cladding materials (e.g.- doped silica and silica glasses) limit the functionality of the optical fibers. Therefore, the optical properties of the fibers, such as phase, polarization state, amplitude, mode profile are fixed and cannot be altered once after the fiber drawing fabrication. The advent of new fabrication technologies for optical nanostructures such as plasmonic and metasurfaces allows us to overcome these limitations by tailoring those optical properties for advanced light manipulation and the development of novel optical fiber devices. In this dissertation, I have reported four main projects on integrating plasmonic and metasurface nanostructures into an optical fiber for novel optical functions. In the first project, I demonstrated in-fiber polarization-dependent color filters by nanopatterning asymmetric metallic metasurface array on the end-facet of polarization-dependent photonic-crystal fibers. The asymmetric cross-typed nanoslit metasurface arrays are fabricated on the core of the optical fiber using a focused ion beam milling technique. Highly polarization- and wavelength-dependent transmission with transmission efficiency ~ 70 % in the telecommunication wavelength observed by launching light into two orthogonal linear polarization states of the fiber. In the second project, I have extended the use of the focused ion beam milling technique to fabricate Berry phase metasurfaces on conventional single-mode optical fiber. A focusing effect has been observed in these metasurface-optical fibers, leading to the development of in-fiber metalens. The third project involves the integration of plasmonic nano-circuits on the facet of polarization-maintaining photonic crystal fiber (PM-PCF) and panda-shaped PM-optical fibers. A Yagi-Uda antenna-coupled low loss plasmonic slot waveguide is directly integrated on the optical fiber by direct milling technique. We demonstrated efficient coupling of light from the fiber core to the plasmonic slot waveguide. The light is then propagated in the plasmonic slot waveguide via the propagation of surface plasmon polaritons and emitted to the far-field in the output antenna located in the cladding. We further extend the design of the complex circuit by integrating multi-channels plasmonic waveguide with different waveguide lengths, polarization splitters, and optical directional coupler (ODC) onto the optical fiber. This project first proof-of-concept demonstration on developing an ultra-compact plasmonic network on the tip of optical fiber for advanced optical communications applications. The final project consists of the study of optical modulation by incorporating vanadium dioxide (VO2) nanocrystals into the air holes of anti-resonant hollow-core photonic crystal fibers (ARHCF). Efficient optical modulation is observed by inducing the insulator-to-metal phase transition of VO2 at different temperatures.Item Characteristic measurements within a GEC rf Reference Cell.(2010-10-08T16:15:25Z) Creel, James Ruell.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.Since its introduction, the GEC rf Reference Cell has provided a baseline for comparison among various experiments performed within the complex (dusty) plasma community. The GEC cell, while providing for data comparison between systems due to its standardized design, does not exist without some variation between cells. In this work, two GEC rf Reference Cells located within the CASPER Hypervelocity Impacts & Dusty Plasmas Lab will be utilized to examine variations in operating parameters. Both standard analysis and Langmuir probe techniques will be employed in an attempt to gain insight into the experimental workings of a standard GEC rf Reference Cell.Item Charging of aggregate grains in astrophysical environments.(2011-12-19) Ma, Qianyu.; Matthews, Lorin Swint.; Physics.; Baylor University. Dept. of Physics.Plasma is a gas in which a portion of particles are ionized. Dust is a ubiquitous component of the universe, and when present in plasma, can form dusty plasma system. Dust in the plasma is generally charged due to the constant collisions with free moving electrons and ions. Cosmic dust can also be charged by other means such as UV and X-ray radiation, and secondary electron emission due to the impact of energetic electrons and ions. The presence of charged dust particles alters the properties of the plasma. The charge on dust grains also affects their dynamics, and influences the coagulation rate. Most previous work assumes that cosmic dust is spherical in shape. However, remote observations and in-situ measurements indicate that cosmic dust is likely to have an aggregate structure. This study examines the charging of aggregate grains in different astrophysical environments. A 3D numerical model employing a self-consistent iterative approach to compute the aggregate charge is introduced. Different size distributions for cosmic dust grains are used in the simulation. The results are compared with previous work on spherical grains, and it is shown that the charging of aggregates differ significantly from that of spheres. Models on predicting charge based on the aggregate structure are proposed, and implications and consequences for future research are discussed.Item Curvature invariants for wormholes and warped spacetimes.(2020-05-01) Mattingly, Brandon John, 1989-; Cleaver, Gerald B.The Carminati and McLenaghan (CM) curvature invariants are powerful tools for probing spacetimes. Henry et al. formulated a method of plotting the CM curvature invariants to study black holes. The CM curvature invariants are scalar functions of the underlying spacetime. Consequently, they are independent of the chosen coordinates and characterize the spacetime. For Class B1 spacetimes, there are four independent CM curvature invariants: R, r1, r2, and w2. Lorentzian traversable wormholes and warp drives are two theoretical solutions to Einstein’s field equations, which allow faster-than-light (FTL) transport. The CM curvature invariants are plotted and analyzed for these specific FTL spacetimes: (i) the Thin-Shell Flat-Face wormhole, (ii) the Morris-Thorne wormhole, (iii) the Thin-Shell Schwarzschild wormhole, (iv) the exponential metric, (v) the Alcubierre metric at constant velocity, (vi) the Natário metric at constant velocity, and (vii) the Natário metric at an accelerating velocity. Plots of the wormhole CM invariants confirm their traversability and show how to distinguish the wormholes. The warp drive CM invariants reveal key features such as a flat harbor in the center of each warp bubble, a dynamic wake for each warp bubble, and rich internal structure(s) of each warp bubble.Item Deflation methods in lattice QCD.(2020-07-20) Whyte, Travis, 1992-; Wilcox, Walter, 1954-The inversion of the Dirac operator is a necessary feature of calculating physical observables within lattice QCD. The calculation of fermionic forces within hybrid Monte Carlo and the formation of quark propagators are two examples where such an inversion is needed. The many discretizations of the Dirac operator pose an algorithmic and computational challenge due to their size and their eigenspectra. As the quark mass approaches its physical value, the low lying eigenspectra of the Dirac operator approaches zero. From this arises the phenomena of critical slowing down, where the number of iterations to obtain an approximate solution for an iterative solver increases as a power law. Deflation and multigrid are two techniques that combat the effects of critical slowing down. We present a deflated multigrid preconditioner of FGMRES for the Wilson-Dirac operator in the lattice Schwinger model. Our method of deflation within the preconditioner demonstrates a remarkable reduction in cost for the inversion of the Wilson-Dirac operator, and also displays very mild scaling with respect to lattice size. The calculation of physical quantities arising from disconnected quark loops is one of the largest challenges in lattice QCD. A direct approach is to calculate the propagator for all lattice sites to all lattice sites. For large lattices, this approach is intractable so stochastic methods are used. The physical signal must be extracted from the noise created by these methods, and thus noise subtraction techniques are mandatory. We present deflation based noise subtraction techniques for the scalar, local vector and non-local vector operators in the quenched approximation at zero quark mass and with the inclusion of dynamical sea quarks at larger than physical pion mass. In both cases, the deflation based methods show dramatic reduction in the variance of these noisy calculations.Item Development of a digital optical diagnostic system for the CASPER GEC rf reference cell.(2006-05-11T20:09:16Z) Boesse, Carolyn M.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.The development and implementation of a completely digital optical analysis system for dusty plasma research has been completed. This system minimizes data loss during acquisition and processing and allows image data to be acquired much more quickly and efficiently than in previous analog methods. The automated camera-lens system has been shown to be successful in imaging plasma discharge regions at a sufficient acquisition rate with multiple images to provide ease of analysis concerning position and velocity of particles and ordering of the crystal lattice. Analysis techniques have been improved due primarily to uncompromised raw data with Matlab providing a unique analysis toolset for processing data via PIV and PTV algorithms. PIV algorithms have been shown to have the advantage of greatly reducing computation time and the ability to calculate particle velocities when individual particles are not resolvable, while PTV algorithms provide more specific information about dust grain interactions and more precise velocity calculations.Item Effects of laser light on argon plasma in a GEC rf reference cell.(2011-09-14) Price, Alexander Thomas.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.Since lasers have become so powerful in dusty plasma research, it is important to determine the manner in which a laser will affect the plasma. In this work, a Verdi ™ G-Series optically pumped semiconductor laser was used in conjunction with a Langmuir probe to determine the effect (if any) that the laser has on the plasma. A Langmuir probe was used to measure and monitor various plasma parameters in a dusty argon plasma. Measurements were taken with the laser immediately beneath the probe at various plasma pressures, plasma powers, and laser powers.Item Electric neutron polarizability and eigenspectrum subtraction techniques for disconnected quark loops.(2011-09-14) Guerrero, Victor Xavier.; Wilcox, Walter, 1954-; Physics.; Baylor University. Dept. of Physics.I present an analysis for the mass shift of the neutron in order to obtain the neutron electric polarizability. Neutron electric polarizability can be studied by implementing a static electric field on the lattice. The implementation of this field, though, is non-trivial and the "proper" form for lattice implementation is studied and the various techniques are presented. Separately, I present the development of new techniques to calculate disconnected quark loops; a quantity that is necessary for many different analyzes but has been shown to be computationally intensive. These new techniques, which use Z(N) noise, utilize the eigenspectrum of the quark matrix to reduce statistical error found in disconnected operators.Item Encrypting the universe.(2017-08-02) Vestal, Lesley, 1991-; Cleaver, Gerald B.Layer one N = 4 SUSY Weakly Coupled Free Fermionic Heterotic String (WCFFHS) Models that include string-scale massive gauge sectors are statistically investigated for even orders through 12 for uniqueness and gauge content. A focus is given to models containing the standard model or gauge group content with the embedded standard model. Results are compared with those of prior searches of N = 4 models without explicit string-scale massive gauge sectors. This search revealed models with standard model gauge content at the string scale, which were not observed in prior searches. Additionally, research regarding an image encryption algorithm is presented. The RGB values of each pixel in an image are encrypted using three intertwined Mandelbrot summations. Runtimes for decryption depend primarily on the size of the image. Modifications to increase complexity and runtime are explored. Advantages include adaptability, reasonable runtime on a typical personal computer and that it is novel, enhancing its security.Item Enhancing hadron jet reconstruction in the CMS Level-1 trigger using machine learning.(2022-05-03) Hasan, Syed Mahedi, 1992-; Brinkerhoff, Andrew.Level–1 Trigger (L1T) algorithms used in the Compact Muon Solenoid (CMS) experiment for detecting different physics objects must be optimized to ensure that CMS continues to collect the most interesting proton–proton collision events for analysis. In this thesis, a new machine learning based approach using boosted decision trees (BDTs) is presented, which improves the jet detection performance in the L1T. In the first step, a BDT is trained using 12 features of L1T jets to generate an importance ranking of the features. The results indicate that a new algorithm for mitigating the effect of simultaneous collisions (‘pileup’) called the ‘phi–ring’ algorithm could be better at detecting L1T jets than the current ‘chunky donut’ algorithm. New BDTs are then trained separately using phi–ring and chunky donut energies as input, to confirm the previous finding. Outputs of the BDTs that use phi–ring energies as input are found to be more stable in energy scale under varying pilepup conditions, with resolution similar to the current jet detection algorithm. Hence, we propose to use the phi–ring algorithm to calibrate jet energies and improve jet detection in the CMS L1T in Run 3 (2022–2025).Item Environmental applications of plasma physics : aerosolized nanoparticle decontamination using an inductively heated plasma device.(2018-04-17) Uppfalt, Katie M., 1991-; Matthews, Lorin Swint.Materials with sizes on the nanometer scale are highly desired for their unique size-dependent properties that prove beneficial in industrial and consumer processes. However, the increased use of nanomaterials could lead to an increased risk of exposure to materials that are detrimental to human health. The link between inhalation of nano-scale particles and diseases of the lungs are of particular concern. In an effort to reduce the risk of exposure to aerosolized nanometer sized particles, a new method is recommended to remove nanoparticles from the air using plasma. It is proposed that the test system subject SiO2 nanoparticles to plasma treatment in an inductively heated plasma generator to study the effectiveness and efficiency of plasma as an aerosolized nanoparticle decontamination mechanism. The treatment system is a multi-step process involving the generation and characterization of nanoparticles and plasma treatment, followed by the collection and disposal or distribution of remaining particles.Item Extremal conditions in early universe cosmology.(2021-10-22) Lee, Jeff S., 1964-; Cleaver, Gerald B.Some aspects of Special Relativity have remained largely unresolved and unexplored even after more than a century since its formulation; this is particularly true in the case of relativistic thermodynamics. Attempts to derive a relativistic temperature transformation have met with limited success, particularly when trying to transform a scalar temperature. Much more credible results have emerged when the inverse temperature (a van-Kampen Israel future-directed timelike 4-vector) was invoked. In this dissertation, the first self-consistent formulations of the relativistic Wien’s Displacement Law and the relativistic Stefan-Boltzmann Law are presented. Also examined is the use of occupation number and the inverse temperature 4-vector to justify temperature inflation of the Cosmic Microwave Background for any relativistic observer. The interaction of the Hawking spectrum of a 1 attometer (10-18 m) primordial black hole with an incoming composite particle reveals that when a primordial black hole reaches the Planck scale, its absorptivity and emissivity cause it to effectively become a white hole for the final instant of its existence.Item Fabrication of a single layer organic photovoltaic device based on an indium-tin-oxide/copper phthalocyanine/aluminum heterostructure.(2007-01-18T17:27:30Z) Jayasinghe, Aroshan.; Park, Kenneth Taesung, 1965-; Physics.; Baylor University. Dept. of Physics.An ultra high vacuum chamber was designed and constructed for the purpose of fabricating organic photovoltaic devices. Thermal vapor deposition of copper phthalocyanine as the active layer and aluminum as the cathode onto a substrate of indium-tin-oxide coated glass was tested in ultra high vacuum conditions. Auger electron spectroscopy was used to analyze the surface properties of the different layers. It was possible to prepare the electrodes to the necessary quality, but the vapor deposition of the organic active layer proved to be unsuccessful. The conductivity of the deposited copper phthalocyanine was much higher than anticipated. Two possible mechanisms for this increase in conductivity are polymerization of the molecules and the formation of stacked assemblies. The residual copper phthalocyanine left in the crucible was examined with a scanning electron microscope and evidence of both mechanisms was observed.Item First search for pair production of scalar top quarks decaying to top quarks and light-flavor jets with low missing transverse momentum.(2020-07-21) Madrid, Christopher Michael, 1993-; Hatakeyama, Kenichi.; Dittmann, Jay R.After the discovery of the Higgs boson in 2012, the current best theoretical model that describes all observed particles and their interactions, the standard model (SM), was considered complete. However, there are a plethora of physical phenomena that the SM does not accurately describe, which motivates particle physicists to search for evidence of new particles produced by high energy collisions at the Large Hadron Collider (LHC). In traditional searches for physics beyond the standard model, a requirement of high missing transverse momentum (ptmiss) is often used to identify potential new particles. However, without any signs of significant deviations from standard model expectations, a search where this requirement is removed has been performed. There are many well motivated and previously unexplored physics models, including versions of supersymmetry (SUSY) characterized by R-parity violation or with additional hidden sectors, that predict the production of events with low ptmiss, many jets, and top quarks. In particular, a general search is performed to look for the pair production of scalar top quarks that would decay to two top quarks and six additional light flavor jets. The search is performed using events with at least seven jets and exactly one electron or muon. No requirement on ptmiss is imposed. With the use of a neural-network-based signal-to-background discriminator, a background estimation has been achieved where more traditional techniques would not be possible. The study is based on a sample of proton-proton collisions at sqrt{s} = 13 TeV corresponding to 137.2 (1/fb) of integrated luminosity collected with the Compact Muon Solenoid (CMS) detector at the LHC in 2016, 2017, and 2018. Results of the search are interpreted for stealth SUSY and SUSY with R-parity violation, resulting in a lower limit exclusion of scalar top production of 900 and 700 GeV, respectively.Item Fundamental particle and wave dynamics in dusty plasmas.(2012-11-29) Zhang, Zhuanhao.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.Dusty plasma is a low-temperature plasma containing dust particles varying in size from nanometers to micrometers. Due to plasma fluxes to its surface, a dust particle will charge negatively or positively depending on the charging mechanism involved. The motion of a dust particle within a dusty plasma can be recorded using a video camera, allowing for examination of the particle dynamics at the kinetic level. Any investigation of dusty plasmas first requires a proper understanding of the fundamental particle-particle interaction, dust particle charge and screening length. Due to the perturbative nature of the majority of diagnostics in common use, all of these are difficult to measure properly. Each of the fundamental parameters mentioned above are addressed in this thesis. First a minimally perturbative technique, allowing experimental detection of each of these parameters, will be introduced. Next, a study of vertically aligned, extended dust particle chains employing a glass box placed on the lower powered electrode in a ground based RF plasma system will be discussed. Finally, by adjusting the discharge power and the gas pressure within the plasma chamber, it will be shown that a chaotic dust cloud can form such vertical chains as well as self-excited dust acoustic waves. An investigation of both the particle and wave dynamics within various sizes of glass box and under a number of plasma conditions will be presented. A theoretical model is also introduced providing a comprehensive dispersion relationship for dust acoustic waves (DAWs) and examining the instabilities resulting from the effects created by the dust temperature, particle charge variation, and ion-drag-force fluctuations. It is shown that each plays a different role depending on the wavelength regime considered.Item Fundamental physics within complex plasmas.(2012-11-29) Douglass, Angela Michelle.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.In this work, both experimental and numerical methods are used to investigate several of the fundamental processes and assumptions commonly found in an earth-based radio-frequency (RF) complex plasma discharge. First the manner in which the dust particle charge varies with the particle’s height above the powered electrode is investigated. Knowledge of the dust particle charge is required to understand nearly all complex plasma experiments since it affects the dust particle’s levitation height and particle-particle interactions. A fluid model which includes effects due to ion flow and electron depletion (which are significant dust charging effects within the sheath where the particles levitate) is employed to determine the plasma parameters required to calculate the dust particle charge. Second, the levitation limits of the dust particles and the structure of the sheath are investigated. The CASPER GEC RF reference cell is used to perform two experiments: one to measure the dust levitation height as a function of applied RF voltage and one to determine the electric force profile. The fluid model is then used to interpret the experimental results. This study provides a better understanding of the sheath structure, particle behavior within the sheath, and provides a new, in situ experimental method for locating the approximate height of the sheath edge in any dusty plasma system. Finally, both molecular dynamics (MD) simulations and an experiment are employed to determine the physical processes that a complex plasma system goes through as it rapidly transitions from a liquid to solid state.Item Gravitational collapse and formation of black holes in the Brans-Dicke theory of gravity with (2+1) dimensions.(2008-03-03T17:23:59Z) Wu, Rui.; Wang, Anzhong.; Physics.; Baylor University. Dept. of Physics.In this thesis, the gravitational collapse of the Brans-Dicke scalar field and formation of black holes in 2+1 Gravity is examined. In contrast to general relativity, there are two conformally related frames in the Brans-Dicke theory: the Jordan frame and the Einstein frame. All the self-similar solutions are first re-derived in three dimensional Brans-Dicke theory, and then their local and global properties are studied by paying particular attention to the formation of black holes due to the gravitational collapse of the scalar field.Item Gravitational radiation and black hole formation from gravitational collapse in theories of gravity with broken Lorentz symmetry.(2019-07-12) Bhattacharjee, Madhurima, 1989-; Wang, Anzhong.Quantum gravity is expected to contain Lorentz symmetry only as an emergent low energy symmetry with the scale at which it is broken presently inaccessible to current experiments. My research, is centered around understanding various physical aspects of gravitational theories that modify general relativity by explicitly breaking Lorentz symmetry (i.e. Hořava-Lifshitz gravity and Einstein-æther theory) in gravitational sector, so that they are consistent with all current observations. In this dissertation I have studied numerically, gravitational collapse of a massless scalar field in Einstein-æther theory showing the existence of outermost “dynamical Universal horizons (dUHs)”. Such a dUH evolves into the causal boundary, even for excitations with arbitrarily large speeds of propagation. I have also studied the gravitational wave solutions in Einstein-æther theory and their behavior, especially how they may be potentially distinguishable by present or future detectors from the standard prediction of general relativity. I have also studied analytically black hole solutions in 2D Hořava gravity (non-projectable) which is non-minimally coupled with a nonrela-tivistic scalar field with focus on understanding Hawking radiation and the properties of the universal horizons.Item Gravitational waves and cosmology.(2021-04-14) Fier, Jared Robert, 1992-; Wang, Anzhong.The recent discovery of GW140915 and the confirmation of the existence of gravitational waves (GWs) has garnered the attention of many physicists as they seek to understand their behavior as they travel across the universe. In this dissertation, one will find the study singularities which may arise in plane GWs, and cosmological perturbations may affect GWs as they propagate through an expanding, inhomogeneous universe. It is found that in the BJR coordinates, singularities arise at the focused point u = us, except in the two cases: (i) α = 1/2, ∀ χn, and (ii) α = 1, χi = 0, where χn are the coefficients in the expansion and α is a parameter. When observing GWs produced from remote astrophysical sources, one finds that there are three scales to consider, λ, Lc, and L which denote the typical wavelength of the GW, the scale of the cosmological perturbations, and the size of the observable universe, respectively. The Einstein equations were calculated for GWs on the cosmic scale, and the geometric optics approximation found the gravitational integrated Sachs-Wolfe effects created by both the cosmological scalar and tensor perturbations.Item Gravitational waves in Einstein-aether theory.(2021-05-24) Zhao, Xiang, 1991-; Wang, Anzhong.We study gravitational waves produced by N-body systems in Einstein-aether theory. In particular, we calculate the gravitational waveforms, polarizations, response functions of the detectors and the radiation power by using the post-Newtonian approximations to the lowest order. Applying the general formulas to three different triple systems with periodic orbits, we find that the scalar mode and the longitudinal mode (hb and hL) are all suppressed by a factor of c14 < O(10−5) with respect to the transverse-traceless modes (h+ and h×), while the vector modes (hX and hY ) are suppressed by a factor of c13 < O(10−15). We also find that gravitational waves depend sensitively on the configurations of the triple systems, their orientations with respect to the detectors, and the binding energies of the three compact bodies. The result for the first relativistic triple system, PSR J0337+1715, shows that the quadrupole emissions in different theories of gravity have almost the same amplitude, but the dipole emission can be as big as the quadrupole emission in Einstein-aether theory. This provides a very promising window to obtain severe constraints on Einstein-aether theory by multi-band gravitational wave astronomy.