Physics Commons^™

Local And Nonlocal Spatial Densities In Quantum Field Theory, R E. Wagner, M R. Ware, E V. Stefanovich, Qichang Su, Rainer Grobe

Faculty publications – Physics

We use a one-dimensional model system to compare the predictions of two different yardsticks to compute the position of a particle from its quantum field theoretical state. Based on the first yardstick (defined by the Newton-Wigner position operator), the spatial density can be arbitrarily narrow, and its time evolution is superluminal for short time intervals. Furthermore, two spatially distant particles might be able to interact with each other outside the light cone, which is manifested by an asymmetric spreading of the spatial density. The second yardstick (defined by the quantum field operator) does not permit localized states, and the time …

Coulomb-Induced Emission Dynamics And Self-Consistent Calculations Of Type-Ii Sb-Containing Quantum Dot Systems, Kamil Gradkowski, Tomasz J. Ochalski, N. Pavarelli, H. Y. Liu, J. Tatebayashi, D. B. Williams, Guillaume Huyet, D. L. Huffaker

Cappa Publications

This paper investigates the effects of Coulomb interactions on the emission dynamics of Sb-containing quantum dot (QD) systems under high excitation densities. Two different type-II confinements are studied: confined electrons with unconfined holes using InAs/GaAs QDs capped with a GaAsSb quantum well (type-IIa), and confined holes with unconfined electrons using GaSb/GaAs QDs capped with an InGaAs quantum well (type-IIb). Time-resolved photoluminescence experiments are compared with self-consistent numerical calculations using an 8-band k·p model. In both structures, we observe a significant blueshift of emission and wavelength-dependent radiative lifetimes, but with marked quantitative differences between the two systems: in the type-IIa, the …

Characterization And Application Of Isolated Attosecond Pulses, Michael Chini

Electronic Theses and Dissertations

Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few-cycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited …

Characterization Of Ceramic Matrix Composite Materials Using Millimeter-Wave Techniques, Matthew Lee Bischoff

Browse all Theses and Dissertations

This thesis describes studies that were carried out on Ceramic Matrix Composite (CMC) materials. These materials were provided by the Air Force Research Laboratory for evaluation in the millimeter-wave frequency region with the goal of developing Non-Destructive Evaluation techniques. This thesis centers on describing the measured reflections from an Oxide/Oxide and SiC/SiNC CMC materials. Models were derived from the Fresnel equations to account for the reflected and transmitted waves in these materials. System models were developed to describe the power coupling of the spectra measured in three separate measurement systems. Using these models the complex index of refraction was determined …

Wettability And “Petal Effect” Of Gaas Native Oxides, A. Gocalinska, Kamil Gradkowski, V. Dimastrodonato, L. O. Mereni, G. Juska, Guillaume Huyet, E. Pelucchi

Cappa Publications

We discuss unreported transitions of oxidised GaAs surfaces between (super)hydrophilic and hydrophobic states when stored in ambient conditions. Contact angles higher than 90° and high adhesive force were observed for several air-aged epitaxial samples grown under different conditions, as well as on epi-ready wafers. Regardless of the morphologies of the surface, superhydrophilicity of oxygen-plasma treated samples was observed, an effect disappearing with storage time. Reproducible hydrophobicity was likewise observed, as expected, after standard HCl surface etching. The relation between surface oxides and hydrophobic/hydrophilic behaviour is discussed.

Causality And Relativistic Localization In One-Dimensional Hamiltonians, R E. Wagner, B T. Shields, M R. Ware, Qichang Su, Rainer Grobe

Faculty publications – Physics

We compare the relativistic time evolution of an initially localized quantum particle obtained from the relativistic Schrodinger, the Klein-Gordon and the Dirac equations. By computing the amount of the spatial probability density that evolves outside the light cone we quantify the amount of causality violation for the relativistic Schrodinger Hamiltonian. We comment on the relationship between quantum field theoretical transition amplitudes, commutators of the fields and their bilinear combinations outside the light cone as indicators of a possible causality violation. We point out the relevance of the relativistic localization problem to this discussion and comment on ideas about the supposed …

Electron-Positron Pair Creation Induced By Quantum-Mechanical Tunneling, M Jiang, W Su, X Lu, Z M. Sheng, Y T. Li, J Zhang, Rainer Grobe, Qichang Su

Faculty publications – Physics

We study the creation of electron-positron pairs from the vacuum induced by two spatially displaced static electric fields. The strength and spatial width of each localized field is less than required for pair creation. If, however, the separation between the fields is less than the quantum-mechanical tunneling length associated with the corresponding quantum scattering system, the system produces a steady flux of electron-positron pairs. We compute the time dependence of the pair-creation probability by solving the Dirac equation numerically for various external field sequences. For the special case of two very narrow fields we provide an analytical expression for the …

Blackbody-Radiation Correction To The Polarizability Of Helium, Mariusz Puchalski, Ulrich D. Jentschura, Peter J. Mohr

Physics Faculty Research & Creative Works

The correction to the polarizability of helium due to blackbody radiation is calculated near room temperature. A precise theoretical determination of the blackbody radiation correction to the polarizability of helium is essential for dielectric gas thermometry and for the determination of the Boltzmann constant. We find that the correction, for not too high temperature, is roughly proportional to a modified hyperpolarizability (two-color hyperpolarizability), which is different from the ordinary hyperpolarizability of helium. Our explicit calculations provide a definite numerical result for the effect and indicate that the effect of blackbody radiation can be excluded as a limiting factor for dielectric …

Excitability In Optically Injected Semiconductor Lasers: Contrasting Quantum- Well- And Quantum-Dot-Based Devices, Bryan Kelleher, C. Bonatto, Guillaume Huyet, Stephen P. Hegarty

Cappa Publications

Excitability is a generic prediction for an optically injected semiconductor laser. However, the details of the phenomenon differ depending on the type of device in question. For quantum-well lasers very complicated multipulse trajectories can be found, while for quantum-dot lasers the situation is much simpler. Experimental observations show the marked differences in the pulse shapes while theoretical considerations reveal the underlying mechanism responsible for the contrast, identifying the increased stability of quantum-dot lasers to perturbations as the root.

Simulation Of Polycapillary And Multichannel Plate X-Ray Optics, Robert Schmitz

Legacy Theses & Dissertations (2009 - 2024)

Simulation of x-ray optical systems is an important tool for optics design for known applications, and optic development for potential applications. Polycapillary optics are thin glass cylinders containing hundreds of thousands of hollow channels that transmit x rays using total external reflection. These optics have been developed for many applications, from beam filtering to x-ray collimating or focusing. A Monte Carlo based ray-tracing simulation was developed to model a wide range of polycapillary optic geometries. The simulation uses a vector-based approach to model all photons and optical geometries in three dimensions. Simulation verification was performed for a wide range of …

Electromagnetic Propagation Anomalies In Waveguiding Structures And Scattering Systems, Alessandro Salandrino

Electronic Theses and Dissertations

The effects related to diffraction and interference are ubiquitous in phenomena involving electromagnetic wave propagation, and are accurately predicted and described within the framework of classical electrodynamics. In the vast majority of the cases the qualitative features of the evolution of a propagating wave can be inferred even without detailed calculations. A field distribution will spread upon propagation, will accumulate phase along the direction of power flow, will exert mechanical forces upon scattering objects in the direction of propagation etc. When such predictions fail, counterintuitive effects and new functionalities can be engineered. In this work a series of exceptional cases …

Time Dilation In Relativistic Two-Particle Interactions, B T. Shields, Rainer Grobe, E V. Stefanovich, M R. Ware, Qichang Su, M C. Morris

Faculty publications – Physics

We study the orbits of two interacting particles described by a fully relativistic classical mechanical Hamiltonian. We use two sets of initial conditions. In the first set (dynamics 1) the system's center of mass is at rest. In the second set (dynamics 2) the center of mass evolves with velocity V. If dynamics 1 is observed from a reference frame moving with velocity-V, the principle of relativity requires that all observables must be identical to those of dynamics 2 seen from the laboratory frame. Our numerical simulations demonstrate that kinematic Lorentz space-time transformations fail to transform particle observables between the …

Characterization Of Pollen Particles Using Lidar, Leda Sox

Graduate Student Posters

We have observed pollen in the local troposphere using the depolarization capabilities of a LIDAR (Light Detection and Ranging) system. The polarization characteristics of the received LIDAR signal, along with supplemental pollen forecast data, allowed me to characterize the shape of the pollen particles.

Space-Time Properties Of A Boson-Dressed Fermion For The Yukawa Model, R E. Wagner, M R. Ware, Q Su, Rainer Grobe

Faculty publications – Physics

We analyze the interaction of fermions and bosons through a one-dimensional Yukawa model. We numerically compute the energy eigenstates that represent a physical fermion, which is a superposition of bare fermionic and bosonic eigenstates of the uncoupled Hamiltonian. It turns out that even fast bare fermions require only low-momentum dressing bosons, which attach themselves to the fast fermion through quantum correlations. We compare the space-time evolution of a physical fermion with that of its bare counterpart and show the importance of using dressed observables. The time evolution of the center of mass as well as the wave packet's spatial width …

Exponential Enhancement Of Field-Induced Pair Creation From The Bosonic Vacuum, R E. Wagner, M R. Ware, Q Su, Rainer Grobe

Faculty publications – Physics

Using numerical solutions to quantum field theory, the creation of boson-antiboson pairs from the vacuum under a very strong localized external electric field is explored. The simulations reveal that the initial linear increase of the number of particles turns into an exponential growth. This self-amplification can be understood as the result of the interaction of the previously generated particles with the creation process. While the number of particles keeps increasing, the spatial shape of the (normalized) charge density of the created particles reaches a universal form that can be related to the bound states of the supercritical potential well. We …

Bosonic Analog Of The Klein Paradox, R E. Wagner, M R. Ware, Q Su, Rainer Grobe

Faculty publications – Physics

The standard Klein paradox describes how an incoming electron scatters off a supercritical electrostatic barrier that is so strong that it can generate electron- positron pairs. This fermionic system has been widely discussed in textbooks to illustrate some of the discrepancies between quantum mechanical and quantum field theoretical descriptions for the pair creation process. We compare the fermionic dynamics with that of the corresponding bosonic system. We point out that the direct counterpart of the Pauli exclusion principle (the central mechanism to resolve the fermionic Klein paradox) is stimulated emission, which leads to the resolution of the analogous bosonic paradox.

A Wearable Head-Mounted Projection Display, Ricardo F. Martins

Electronic Theses and Dissertations

Conventional head-mounted projection displays (HMPDs) contain of a pair of miniature projection lenses, beamsplitters, and miniature displays mounted on the helmet, as well as a retro-reflective screen placed strategically in the environment. We have extened the HMPD technology integrating the screen into a fully mobile embodiment. Some initial efforts of demonstrating this technology has been captured followed by an investigation of the diffraction effects versus image degradation caused by integrating the retro-reflective screen within the HMPD. The key contribution of this research is the conception and development of a mobileHMPD (M-HMPD). We have included an extensive analysis of macro- and …

Pair Creation Rates For One-Dimensional Fermionic And Bosonic Vacua, T Cheng, M R. Ware, Q Su, Rainer Grobe

Faculty publications – Physics

We compare the creation rates for particle-antiparticle pairs produced by a supercritical force field for fermionic and bosonic model systems. The rates obtained from the Dirac and Klein-Gordon equations can be computed directly from the quantum-mechanical transmission coefficients describing the scattering of an incoming particle with the supercritical potential barrier. We provide a unified framework that shows that the bosonic rates can exceed the fermionic ones, as one could expect from the Pauli-exclusion principle for the fermion system. This imbalance for small but supercritical forces is associated with the occurrence of negative bosonic transmission coefficients of arbitrary size for the …

Creation Of Multiple Electron-Positron Pairs In Arbitrary Fields, T Cheng, Q Su, Rainer Grobe

Faculty publications – Physics

We examine the spontaneous breakdown of the matter vacuum triggered by an external force of arbitrary strength and spatial and temporal variations. We derive a nonperturbative framework that permits the computation of the complete time evolution of various multiple electron-positron pair probabilities. These time-dependent probabilities can be computed from a generating function as well as from solutions to a set of ratelike equations with coupling constants determined by the single-particle solutions to the time-dependent Dirac equation. This approach might be of relevance to the planned experiments to observe for the first time the laser-induced breakdown process of the vacuum.

Effective Medium Theory, Rough Surfaces, And Moth’S Eyes, David D. Allred, Zephne Larsen, Joseph Muhlestein, R. Steven Turley, Anthony Willey

Faculty Publications

Optics in the extreme ultraviolet (XUV) have important applications in microelectronics, microscopy, space physics, and in imaging plasmas. Because of the short wavelengths involved in these applications, it is critical to account for interfacial roughness to accurately predict the reflection and absorption of XUV optics. This paper examines two possible effects of roughness on optical absorption, non-specular reflection and enhanced transmission and compares these to measured experimental data on a rough Y2O3 thin film.

Limitations Of Decomposition-Based Imaging Of Longitudinal Absorber Configurations, S D. Campbell, S D. Grobe, I L. Goodin, Q Su, Rainer Grobe

Faculty publications – Physics

We examine theoretically and experimentally an imaging scheme that uses the transverse intensity profile of the scattered light to reconstruct the locations of absorbers embedded in a turbid medium. This method is based on an a priori knowledge of the scattered light patterns associated with a single absorber that is located at various positions inside the medium. We discuss the range of validity of this method, and its sensitivity with regard to noise, and propose an algorithm to improve its accuracy.

Decomposition-Based Recovery Of Absorbers In Turbid Media, S D. Campbell, I L. Goodin, S D. Grobe, Qichang Su, Rainer Grobe

Faculty publications – Physics

We suggest that the concept of the point-spread function traditionally used to predict the blurred image pattern of various light sources embedded inside turbid media can be generalized under certain conditions to predict also the presence and location of spatially localized absorbing inhomogeneities based on shadow point-spread functions associated with each localized absorber in the medium. The combined image obtained from several absorbers can then be decomposed approximately into the arithmetic sums of these individual shadow point-spread functions with suitable weights that can be obtained from multiple-regression analysis. This technique permits the reconstruction of the location of absorbers.

Design And Application Of Near Infrared Tunable Filter For Atst And Nst, Jun Ma

Dissertations

This thesis includes the following sections: a general design of the Near Infrared Tunable Filter (NIRTF) of Advanced Technology Solar Telescope (ATST) project and the Near Infrared Imaging Magnetograph (IRIM) of the New Solar Telescope (NST), the design of achromatic waveplates, the narrowband continuum observation of a Sunspot at 1.56 µm using IRIM instruments, and the coronal hole observation using the Digital Vector Magnetograph (VMG) at Big Bear Solar Observatory (BBSO).

A near infrared tunable filter system is designed with detailed optical parameters for each component in the system. Among these components, the achromatic waveplates, which used to be an …

Classical-Quantum Correspondence In Electron-Positron Pair Creation, N I. Chott, Qichang Su, Rainer Grobe

Faculty publications – Physics

We examine the creation of electron-positron pairs in a very strong force field. Using numerical solutions to quantum field theory we calculate the spatial and momentum probability distributions for the created particles. A comparison with classical mechanical phase space calculations suggests that despite the fully relativistic and quantum mechanical nature of the matter creation process, most aspects can be reproduced accurately in terms of classical mechanics.

Velocity Half-Sphere Model For Multiple Scattering In A Semi-Infinite Medium, S Menon, Q Su, Rainer Grobe

Faculty publications – Physics

We show how the velocity half-sphere model [S. Menon, Q. Su, and R. Grobe, Phys. Rev. E 72, 041910 (2005)] recently introduced to predict the propagation of light for an infinite turbid medium can be extended to account for the emission of multiply scattered light for a geometry with a planar boundary. A comparison with exact solutions obtained from Monte Carlo simulations suggests that this approach can improve the predictions of the usual diffusion theory for both isotropic and highly forward scattering media with reflecting interfaces.

Nonlocal Entanglement Of Coherent States, Complementarity, And Quantum Erasure, Christopher C. Gerry, Rainer Grobe

Faculty publications – Physics

We describe a nonlocal method for generating entangled coherent states of a two-mode field wherein the field modes never meet. The proposed method is an extension of an earlier proposal [C. C. Gerry, Phys. Rev. A 59, 4095 (1999)] for the generation of superpositions of coherent states. A single photon injected into a Mach-Zehnder interferometer with cross-Kerr media in both arms coupling with two external fields in coherent states produces entangled coherent states upon detection at one of the output ports. We point out that our proposal can be alternatively viewed as a "which path" experiment, and in the case …

Unitary And Nonunitary Approaches In Quantum Field Theory, K D. Lamb, Christopher C. Gerry, Rainer Grobe

Faculty publications – Physics

We use a simplified essential state model to compare two quantum field theoretical approaches to study the creation of electron-positron pairs from the vacuum. In the unitary approach the system is characterized by a state with different numbers of particles that is described by occupation numbers and evolves with conserved norm. The nonunitary approach can predict the evolution of wave functions and density operators with a fixed number of particles but time-dependent norms. As an example to illustrate the differences between both approaches, we examine the degree of entanglement for the Klein paradox, which describes the creation of an electron-positron …

Temperature-Driven Transition From The Wigner Crystal To The Bond-Charge-Density Wave In The Quasi-One-Dimensional Quarter-Filled Band, R. T. Clay, Rahul Hardikar, S. Mazumdar

Scholarship and Professional Work - LAS

It is known that within the interacting electron model Hamiltonian for the one-dimensional 1/4-filled band, the singlet ground state is a Wigner crystal only if the nearest-neighbor electron-electron repulsion is larger than a critical value. We show that this critical nearest-neighbor Coulomb interaction is different for each spin subspace, with the critical value decreasing with increasing spin. As a consequence, with the lowering of temperature, there can occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls state that is a bond-charge-density wave with charge occupancies different from the Wigner crystal. This transition is possible because spin excitations …

Timing Of Pair Production In Time-Dependent Force Fields, Christopher C. Gerry, Q Su, Rainer Grobe

Faculty publications – Physics

We examine the creation and annihilation dynamics for electron-positron pairs in a time-dependent but subcritical electric force using a simplified model system. Numerical and semianalytical solutions to computational quantum field theory show that despite the continuity of the quantum field operator in time, the actual number of created particles can change in a discontinuous way if the field changes abruptly. The number of permanently created particles after the pulse, however, increases continuously with the duration of the electric field pulse, suggesting a transition from an exclusive annihilation to a creation regime.

Electron-Impact Ionization Of L-Shell Atomic Species, Abul Kalam Fazlul Haque, M A. Uddin, A K. Basak, Khondkar R. Karim, B C. Saha, F B. Malik

Faculty publications – Physics

Electron impact ionization cross sections (EIICS) of 30 L-shell targets, with open- and closed-shell configurations in the isoelectronic sequences ranging from Li to Ne, are evaluated using the generalized parameters of our recent modification of BELL formula (MBELL) [Haque , Phys. Rev. A 73, 012708 (2006)]. Three sets of parameters, one each for the 1s, 2s, and 2p orbits, provide an excellent account of the experimental EIICS data of atomic targets, neutral and ionic, up to the atomic number Z=92 and incident energies up to about 250 MeV. In comparison with the quantum mechanical predictions, it is found that the …