Atomic, Molecular and Optical Physics Commons^™

Well-Posedness Of Characteristic Evolution In Bondi Coordinates, Maria Babiuc-Hamilton, Jeff Winicour

Physics Faculty Research

Gravitational waves carry information about their source, and their detection will uncover facets of our universe, otherwise invisible. Recently, we made publicly available a waveform computation tool, the PITT code, as part of the Einstein Toolkit open software for relativistic astrophysics. The code implements the “characteristic method,” which computes the gravitational waves infinitely far from their source in terms of compactified light cones. We proved that our code produces waveforms that satisfy the demands of next generation detectors. However, the main problem is that the well-posedness of the Einstein equations in characteristic formulation is not proven. Here we present …

Computational Renormalization Scheme For Quantum Field Theories, Rainer Grobe, Qichang Su, R E. Wagner

Faculty publications – Physics

We propose an alternative technique for numerically renormalizing quantum field theories based on their Hamiltonian formulation. This method is nonperturbative in nature and, therefore, exact to all orders. It does not require any correlation functions or Feynman diagrams. We illustrate this method for a model Yukawa-like theory describing the interaction of electrons and positrons with model photons in one spatial dimension. We show that, after mass renormalization of the fermionic and bosonic single-particle states, all other states in the Fock space have finite energies, which are independent of the momentum cutoff.

Asymmetries In Production Of He+(N = 2) With An Intense Few-Cycle Attosecond Pulse, Jean Marcel Ngoko Djiokap, S. X. Hu, Wei-Chao Jiang, Liang-You Peng, Anthony F. Starace

Anthony F. Starace Publications

By solving the two-electron time-dependent Schrödinger equation, we study carrier-envelope-phase (CEP) effects on ionization plus excitation of He to He⁺(n = 2) states by a few-cycle attosecond pulse with a carrier frequency of 51 eV. For most CEPs the asymmetries in the photoelectron angular distributions with excitation of He⁺(2s) or He⁺(2p) have opposite signs and are two orders of magnitude larger than for ionization without excitation. These results indicate that attosecond pulse CEP effects may be significantly amplified in correlated two-electron ionization processes.

Systematic Effects In Interferometric Observations Of The Cosmic Microwave Background Polarization, Ata Karakci, Le Zhang, P. M. Sutter, Emory F. Bunn, Andrei Korotkov, Peter Timbie, Gregory S. Tucker, Benjamin D. Wandelt

Physics Faculty Publications

The detection of the primordial B-mode spectrum of the polarized cosmic microwave background (CMB) signal may provide a probe of inflation. However, observation of such a faint signal requires excellent control of systematic errors. Interferometry proves to be a promising approach for overcoming such a challenge. In this paper we present a complete simulation pipeline of interferometric observations of CMB polarization, including systematic errors. We employ two different methods for obtaining the power spectra from mock data produced by simulated observations: the maximum likelihood method and the method of Gibbs sampling. We show that the results from both methods …

Spatiotemporal Fluorescent Detection Measurements Using Embedded Waveguide Sensors, Mark C. Harrison, Andrea M. Armani

Engineering Faculty Articles and Research

Integrated waveguide biosensors, when combined with fluorescent labeling, have significantly impacted the field of biodetection. While there are numerous types of waveguide sensors, the fundamental excitation method is fairly consistent: the evanescent field of the waveguide excites a fluorophore whose emission is detected, either directly via imaging or indirectly via a decrease in power transfer. Recently, a sensor device was demonstrated which is able to back-couple the emitted light into the waveguide, allowing the signal to be detected directly. However, this previous work focused on the development of an empirical model, leaving many theoretical questions unanswered. Additionally, the results from …

Tilt Angle And Birefringence Of Smectic Liquid Crystal Materials, Taylor Van Winkle

Physics

No abstract provided.

Maximum Likelihood Analysis Of Systematic Errors In Interferometric Observations Of The Cosmic Microwave Background, Le Zhang, Ata Karakci, Paul M. Sutter, Emory F. Bunn, Andrei Korotkov, Peter Timbie, Gregory S. Tucker, Benjamin D. Wandelt

Physics Faculty Publications

We investigate the impact of instrumental systematic errors in interferometric measurements of the cosmic microwave background (CMB) temperature and polarization power spectra. We simulate interferometric CMB observations to generate mock visibilities and estimate power spectra using the statistically optimal maximum likelihood technique. We define a quadratic error measure to determine allowable levels of systematic error that does not induce power spectrum errors beyond a given tolerance. As an example, in this study we focus on differential pointing errors. The effects of other systematics can be simulated by this pipeline in a straightforward manner. We find that, in order to accurately …

Theoretical Modeling Of Near-Threshold Shape Resonance Behaviour In Photodetachment Experiments, Laurentiu Dan Dumitriu

Masters Theses

This thesis attempts to better understand the results obtained from photodetachment experiments of Fe-, made by the Western Michigan University experimental atomic physics group at the Advanced Light Source (ALS), Lawrence Berkeley National laboratory.

After a relevant description of the quantum mechanics and theoretical atomic physics concepts and formulas involved in this subject, a physically realistic model, based on the square well potential, is developed. Based on this model, the theoretical photodetachment cross section is computed in order to reproduce the qualitative behavior of the experimental photodetachment cross section measured at ALS.

This development, involving programming in Fortran and numerical …

Why Do Molecules Echo Atomic Periodicity?, Ray Hefferlin, Jonathan Sackett, Jeremy Tatum

Faculty Works

Franck–Condon factors are investigated for sequences of free

main-group diatomic molecules. Theory-based Condon loci

(parabolas) and Morse-potential loci are plotted on Deslandres

tables to verify if they, indeed, follow the largest Franck–Condon

factors. Then, the inclination angles of the Condon loci

are determined. Thus, entire band systems are quantified by

one variable, the angle. For all available isoelectronic sequences,

this angle increases from a central minimum toward

magic-number molecular boundaries. The theory for the Condon

locus gives the angle in terms of the ratio of the upperstate

to the lower-state force constants. It is concluded that

the periodicity is caused …

Effects Of Electric And Magnetic Fields On Moving Liquid Paint On A Glass Surface, John J. Blalock

Theses & Honors Papers

A Tesla coil is a special type of step-up transformer. It takes an input current at a given frequency and voltage, increases the frequency and voltage via resonant induc­ tive coupling, and outputs a very high frequency, high voltage current . While it was originally intended as a means of wirelessly transferring energy, the output from a Tesla coil been used in the arts to move paint around on a glass surface using extremely high voltages on the order of 1 megavolt (MV) or 1000000 volts (V). The aim of this project was to scientifically determine what these mechanisms are …

Forensic Investigation Of Stamped Markings Using A Large-Chamber Scanning Electron Microscope And Computer Analysis For Depth Determination, Eric Douglas Jones

Masters Theses & Specialist Projects

All firearms within the United States are required by the Gun Control Act to be physically marked with a serial number; which is at least 0.003” in depth and 1/16” in height. The purpose of a serial number is to make each firearm uniquely identifiable and traceable. Intentional removal of a serial number is a criminal offense and is used to hide the identity and movements of the involved criminal parties. The current standard for firearm serial number restoration is by chemical etching; which is time & labor intensive as well as destructive to the physical evidence (firearm). It is …

Novel Materials For Use In Homeland Security Research, Jason Osgood Ewen Young

Masters Theses & Specialist Projects

Organometallic pyridazines and compounds derived from them have been of interest in polymer research due to their atypical environmental stability (as compared to other non-aromatic organic semiconductors) as well as their conductivity. The off-metal synthesis and characterization of several pyridazyl thallium, manganese, and rhenium complexes, beginning with fulvenes 1,2- C5H3(COHR)(COR), are reported here. The diacyl fulvenes were treated with hydrazine hydrate to ring close to pyridazines. Next, the pyridazines were converted to their respective thallium salts through treatment with thallium (I) ethoxide. Lastly, the salts were transmetallated into the respective rhenium or manganese complexes through treatment with the respective metal …

Experimenting With Polymer Blend Solar Cells And Active Layer Thickness, Ryan Blumenthal

Physics

Bulk heterojunction organic photovoltaics utilize the electrical characteristics of semi-conductive polymers. These solution processable materials are beneficial because of their low material cost, light weight, and simple fabrication requirements. Our devices employ multiple photoactive polymers, P3HT and PCPDTBT, to absorb photons over a wide spectral range. We optimized various device characteristics including thickness and thermal anneal usage to reach a power conversion efficiency of 3.0% in AM1.5 sunlight. Device performance degrades over time due to atmospheric water and oxygen, prompting us to investigate device packaging to extend cell lifetime for additional testing.

Active Galactic Nuclei Mergers And Outflows: Observations From Optical And Ultraviolet Emission Lines, Robert Scott Barrows

Graduate Theses and Dissertations

I have investigated the nature of a subset of active galactic nuclei (AGN) which show double peaks in their characteristic optical and ultraviolet emission lines. I have performed this investigation through studies of the broad emission line regions (BLRs), which are produced less than 1 pc from the central supermassive black hole (SMBH), and the narrow emission line regions (NLRs), which originate at larger (kpc) distances. The BLR studies consist of detailed line modeling of two individual quasars with double-peaked broad emission line profiles. The modeling suggests there are two primary interpretations of the complex broad line profiles. The first …

Enhancement Of Electron-Positron Pair Creation Due To Transient Excitation Of Field-Induced Bound States, M Jiang, Q Z. Lv, Z M. Sheng, Rainer Grobe, Qichang Su

Faculty publications – Physics

We study the creation of electron-positron pairs induced by two spatially separated electric fields that vary periodically in time. The results are based on large-scale computer simulations of the time-dependent Dirac equation in reduced spatial dimensions. When the separation of the fields is very large, the pair creation is caused by multiphoton transitions and mainly determined by the frequency of the fields. However, for small spatial separations a coherence effect can be observed that can enhance or reduce the particle yield compared to the case of two infinitely separated fields. If the travel time for a created electron or positron …

Balconies, Joe Guimera

The Transdisciplinary STEAM+ Journal

Recent developments in theoretical physics suggest the possibility of parallel universes. What if we could see two or more universes at the same time? In effect, superimpose a scene from one universe; say a street corner, over the image of the same scene from a second universe? The photograph “Balconies” imagines the possibilities.

Discrimination Between Child And Adult Forms Using Radar Frequency Signature Analysis, Stephanie R. Keith

Theses and Dissertations

In this thesis we develop a method to discriminate between adult and child radar signatures. In particular, we examine radar data measured from behind a wall, which introduces radar signal attenuation and multipath effects. To investigate the child/adult discrimination problem in a through-wall, multipath scenario, a previously developed free-space human scattering model was expanded to incorporate multiple paths, and the effects of transmission through, and reflections from, walls and ground. The ground was modeled as a perfectly reflecting surface, while the walls were modeled as homogeneous concrete slabs. Twenty-five reflection paths were identified, involving the direct paths, as well as …

Discrimination Of Neutral Postures In Computer Based Work, Alanna R. Keith

Theses and Dissertations

A biometric system recognizes users based on the way they physically interact with the system. In this work, we discover a common behavior that a typist consistently displays in non-trivial computer work. We sought to demonstrate three objectives: first, compelling proof that a user can be actively recognized over the course of a lengthy task via a neutral posture struck multiple times in that task; two, a sensing concept for capturing the neutral posture, and, third, an objective method for determine the level of work performed by each typist. This thesis develops a model for hand tracking using a simple …

Nested Gaussian Laser Beams - A Blue-Detuned One-Dimensional Lattice Of Optical Dipole Traps For Quantum Computing, Travis Daniel Frazer

Physics

No abstract provided.

Experimental Investigation Of Long-Lived Rydberg States In Ultracold Argon, G. Ranjit, C. I. Sukenik

Physics Faculty Publications

We report on our investigation of the formation and survival of long-lived Rydberg states in argon produced by pulsed laser excitation of ultracold metastable state argon atoms in a magneto-optical trap. The states studied have a 2P1/2 core. Low angular momentum Rydberg states with this core normally autoionize rapidly. If, however, atoms are excited in the presence of electric fields, higher angular momentum states, traditionally termed ZEKE states (ZEKE is derived from zero kinetic energy) can be formed. The lifetime of these states can be orders of magnitude greater than low angular momentum states. In this paper, we report on …

Strain-Mediated Elastic Coupling In Magnetoelectric Nickel/Barium-Titanate Heterostructures, Robert Streubel, Denny Köhler, Rudolf Schäfer, Lukas M. Eng

Robert Streubel Papers

Multiferroic nanomaterials bear the potential for assembling a manifold of novel and smart devices. For room temperature (RT) applications, however, only the BiFeO3 single-phase perovskites are potential candidates to date. Nevertheless, vertical heterostructures separating magnetic and ferroelectric functionality into different layers are now widely proposed to circumvent this lack in materials' availability. We show here that the second approach is very profitable as illustrated by the strain-mediated coupling between such two layers, i.e., a ferroelectric barium titanate single-crystal (BTO) and a magnetostrictive nickel (Ni) thin film. Applying an electric field across the BTO substrate forces the magnetic easy axis in …

Pair Creation For Bosons In Electric And Magnetic Fields, Q Z. Lv, A C. Su, M Jiang, Rainer Grobe, Qichang Su

Faculty publications – Physics

By solving the quantum field theoretical version of the Klein-Gordon equation numerically, we study the creation process for charged boson-antiboson pairs in static electric and magnetic fields. The fields are perpendicular to each other and spatially localized along the same direction, which permits us to study the crucial impact of the magnetic field's spatial extension on dynamics. If its width is comparable to that of the electric field, we find a magnetically induced Lorentz suppression of the pair-creation process. When the width is increased such that the created bosons can revisit the interaction region, we find a region of exponential …

Guided Wave-Based J-Integral Estimation For Dynamic Stress Intensity Factors Using 3d Scanning Laser Doppler Vibrometry, J. Ayers, Christopher Todd Owen, Eric D. Swenson, Anindya Ghoshal, V. Weiss

Faculty Publications

The application of guided waves to interrogate remote areas of structural components has been researched extensively in characterizing damage. However, there exists a sparsity of work in using piezoelectric transducer-generated guided waves as a method of assessing stress intensity factors (SIF). This quantitative information enables accurate estimation of the remaining life of metallic structures exhibiting cracks, such as military and commercial transport vehicles. The proposed full wavefield approach, based on 3D laser vibrometry and piezoelectric transducer-generated guided waves, provides a practical means for estimation of dynamic stress intensity factors (DSIF) through local strain energy mapping via the J-integral. Strain energies …

Adherent Cells Avoid Polarization Gradients On Periodically Poled Litao3 Ferroelectrics, Christof Christophis, Elisabetta Ada Cavalcanti-Adam, Maximilian Hanke, Kenji Kitamura, Alexei Gruverman, Michael Grunze, Peter A. Dowben, Axel Rosenhahn

Peter Dowben Publications

The response of fibroblast cells to periodically poled LiTaO₃ ferroelectric crystals has been studied. While fibroblast cells do not show morphological differences on the two polarization directions, they show a tendency to avoid the field gradients that occur between polarization domains of the ferroelectric. The response to the field gradients is fully established after one hour, a time at which fibroblasts form their first focal contacts. If suspension cells, with a lower tendency to establish strong surface contacts are used, no influence of the field gradients is observed.

On-Chip Non-Reciprocal Optical Devices Based On Quantum Inspired Photonic Lattices, Ramy El-Ganainy, A. Eisfeld, Miguel Levy, Demetrios N. Christodoulides

Department of Physics Publications

We propose integrated optical structures that can be used as isolators and polarization splitters based on engineered photonic lattices. Starting from optical waveguide arrays that mimic Fock space (quantum state with a well-defined particle number) representation of a non-interacting two-site Bose Hubbard Hamiltonian, we show that introducing magneto-optic nonreciprocity to these structures leads to a superior optical isolation performance. In the forward propagation direction, an input TM polarized beam experiences a perfect state transfer between the input and output waveguide channels while surface Bloch oscillations block the backward transmission between the same ports. Our analysis indicates a large isolation ratio …

Simulation Of Charge Transport In Multi-Island Tunneling Devices: Application To Disordered One-Dimensional Systems At Low And High Biases, Madhusudan A. Savaikar, Douglas R. Banyai, Paul Bergstrom, John A. Jaszczak

Department of Physics Publications

Although devices have been fabricated displaying interesting single-electron transport characteristics, there has been limited progress in the development of tools that can simulate such devices based on their physical geometry over a range of bias conditions up to a few volts per junction. In this work, we present the development of a multi-island transport simulator, MITS, a simulator of tunneling transport in multi-island devices that takes into account geometrical and material parameters, and can span low and high source-drain biases. First, the capabilities of MITS are demonstrated by modeling experimentaldevices described in the literature, and showing that the simulated device …

Proton Transfer In Surface-Stabilized Chiral Motifs Of Croconic Acid, Donna A. Kunkel, James Hooper, Scott Simpson, Geoffrey Rojas, Stephen Ducharme, Timothy Usher, Eva Zurek, Axel Enders

Stephen Ducharme Publications

The structure and cooperative proton ordering of two-dimensional sheets of croconic acid were studied with scanning tunneling microscopy and first-principles calculations. Unlike in the crystalline form, which exhibits a pleated, densely packed polar sheet structure, the confinement of the molecules to the surface results in hydrogenbonded chiral clusters and networks. First-principles calculations suggest that the surface stabilizes networks of configurational isomers, which arise from direct hydrogen transfer between their constituent croconic acid monomers. Some of these configurations have a net polarization. It is demonstrated through constrained molecular dynamics simulations that simultaneous proton transfer between any two molecules can occur spontaneously. …

Optically Pumped Spin-Exchange Polarized-Electron Source, Munir Pirbhai, J. Knepper, E. T. Litaker, D. Tupa, Timothy J. Gay

Timothy J. Gay Publications

We describe the operation of a prototype polarized-electron source. Rubidium vapor, contained in a cell, is optically pumped in the presence of a buffer gas. Unpolarized electrons from a tungsten filament are injected into the cell and extracted after undergoing spin exchange with the Rb atoms. We compare the performance of the source when different buffer gases are used. We measure a decrease in electron polarization as their injection energy increases, but find an unexpected regime at higher injection energies yielding increased electron polarization accompanied by a 40-fold increase in current, suggesting the production of slow secondary electrons in the …

Infrared Phonon Modes In Multiferroic Single-Crystal Fete2o5br, K. H. Miller, X. S. Xu, H. Berger, V. Cracium, Xiaoxiang Xi, C. Martin, G. L. Carr, D. B. Tanner

Xiaoshan Xu Papers

Reflection and transmission as a function of temperature (7–300 K and 5–300 K respectively) have been measured on single crystals of the multiferroic compound FeTe₂O₅Br utilizing light spanning from the far infrared to the visible. The complex dielectric function and other optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. Analysis of the anisotropic excitation spectra via Drude-Lorentz fitting and lattice dynamical calculations have led to the observation of 43 of the 53 modes predicted along the b axis of the monoclinic cell. The phonon response parallel to the a and …

Growth Diagram Of La0.7sr0.3mno3 Thin Films Using Pulsed Laser Deposition, Hangwen Guo, Dali Sun, Wenbin Wang, Zheng Gai, Ivan Kravchenko, Jian Shao, Lu Jiang, Thomas Z. Ward, Paul C. Snijders, Lifeng Yin, Jian Shao, Xiaoshan Xu

Xiaoshan Xu Papers

An experimental study was conducted on controlling the growth mode of La_0.7Sr_0.3MnO₃ thin films on SrTiO₃ substrates using pulsed laser deposition (PLD) by tuning growth temperature, pressure, and laser fluence. Different thin film morphology, crystallinity, and stoichiometry have been observed depending on growth parameters. To understand the microscopic origin, the adatom nucleation, step advance processes, and their relationship to film growth were theoretically analyzed and a growth diagram was constructed. Three boundaries between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric and non-stoichiometric growth were identified in the growth diagram. A good …