Atomic, Molecular and Optical Physics Commons^™

Improvement For Generating High-Order Harmonics And Attosecond Pulses With Ultrashort Laser Fields, Dian Peng

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Nonlinear processes of high-order harmonic generation (HHG) produced by ultrashort few-cycle laser pulses possess interesting features which HHG produced by long pulses of many cycles may not have. First, HHG spectra produced by ultrashort pulses are extremely sensitive to the driving pulse waveform, which can be controlled by laser parameters such as carrier-envelope phases (CEPs), time delays or frequency chirps. Second, HHG spectra produced by ultrashort pulses can exhibit broad uneven peaks which are different from usual odd-ordered harmonic peaks that long pulses produce.

Based on the high sensitivity on pulse waveform of HHG spectra produced by ultrashort pulses, we …

Smooth Flow In Diamond: Atomistic Ductility And Electronic Conductivity, Chang Liu, Xianqi Song, Quan Li, Yanming Ma, Changfeng Chen

Physics & Astronomy Faculty Research

Diamond is the quintessential superhard material widely known for its stiff and brittle nature and large electronic band gap. In stark contrast to these established benchmarks, our first-principles studies unveil surprising intrinsic structural ductility and electronic conductivity in diamond under coexisting large shear and compressive strains. These complex loading conditions impede brittle fracture modes and promote atomistic ductility, triggering rare smooth plastic flow in the normally rigid diamond crystal. This extraordinary structural change induces a concomitant band gap closure, enabling smooth charge flow in deformation created conducting channels. These startling soft-and-conducting modes reveal unprecedented fundamental characteristics of diamond, with profound …

Characterization Of Argon And Ar/Cl2 Plasmas Used For The Processing Of Niobium Superconducting Radio-Frequency Cavities, Jeremy J. Peshl

Physics Theses & Dissertations

The plasma processing of superconducting radio-frequency (SRF) cavities has shown significant promise as a complementary or possible replacement for the current wet etch processes. Empirical relationships between the user-controlled external parameters and the effectiveness of Reactive Ion Etching (RIE) for the removal of surface layers of bulk niobium have been previously established. However, a lack of a physical description of the etching discharge, particularly as the external parameters are varied, limits the development of this technology. A full understanding of how these external parameters affect both the amount of material removed and the physical properties of the plasma would aid …

Gamma-Ray Bursts Induced By Turbulent Reconnection, A. Lazarian, Bing Zhang, Siyao Xu

Physics & Astronomy Faculty Research

We revisit the Internal-Collision-induced MAgnetic Reconnection and Turbulence model of gamma-ray bursts (GRBs) in view of the advances made in understanding of both relativistic magnetic turbulence and relativistic turbulent magnetic reconnection. We identify the kink instability as the most natural way of changing the magnetic configuration to release the magnetic free energy through magnetic reconnection, as well as driving turbulence that enables fast turbulent reconnection. We show that this double role of the kink instability is important for explaining the prompt emission of GRBs. Our study confirms the critical role that turbulence plays in boosting reconnection efficiency in GRBs and …

Obituary: Anthony Starace (1945-2019)

Anthony F. Starace Publications

Anthony Starace, George Holmes University Professor of physics, died Sept. 5 from complications related to pancreatitis. He was 74.

Starace was born July 24, 1945, in the Queens borough of New York City. He graduated from Stuyvesant High School and earned his bachelor’s degree from Columbia University in 1966 before moving west to the University of Chicago, where he earned his doctorate under adviser Ugo Fano in 1971. It was in Chicago that he met Katherine Fritz of Beatrice, Nebraska, his wife of 51 years.

Following a postdoctoral appointment at Imperial College London, Starace moved to Lincoln as an assistant …

Generation And Stability Of Structurally Imprinted Target Skyrmions In Magnetic Multilayers, Noah Kent, Robert Streubel, Charles Henri Lambert, Alejandro Ceballos, Soong Gun Je, Scott Dhuey, Mi Young Im, Felix Büttner, Frances Hellman, Sayeef Salahuddin, Peter Fischer

Robert Streubel Papers

Target Skyrmions (TSks) are extended topological spin textures with a constant chirality where the rotation of the z component of the magnetization is larger than π. TSks have topological charge 1 or 0, if the z component of the magnetization Mz goes through a rotation of nπwhere n is an odd or even integer, respectively. TSks with a rotation of the z component of up to 4πhave been imaged via high spatial resolution element-specific X-ray imaging. The TSks were generated by weakly coupling 30 nm thin Permalloy (Ni80Fe20, PY) disks with a 1 μm diameter to asymmetric (Ir 1 nm/Co …

Quantitative Analysis Of Cerium-Gallium Alloys Using A Hand-Held Laser Induced Breakdown Spectroscopy Device, Ashwin P. Rao, Matthew Cook, Howard L. Hall, Michael B. Shattan

Faculty Publications

A hand-held laser-induced breakdown spectroscopy device was used to acquire spectral emission data from laser-induced plasmas created on the surface of cerium-gallium alloy samples with Ga concentrations ranging from 0–3 weight percent. Ionic and neutral emission lines of the two constituent elements were then extracted and used to generate calibration curves relating the emission line intensity ratios to the gallium concentration of the alloy. The Ga I 287.4-nm emission line was determined to be superior for the purposes of Ga detection and concentration determination. A limit of detection below 0.25%was achieved using a multivariate regression model of the Ga I …

Femtosecond Gas-Phase Mega-Electron-Volt Ultrafast Electron Diffraction, Xiaozhe Shen, J. P.F. Nunes, J. Yang, R. K. Jobe, R. K. Li, Ming Fu Lin, B. Moore, M. Niebuhr, S. P. Weathersby, T. J.A. Wolf, C. Yoneda, Markus Guehr, Martin Centurion, X. J. Wang

Martin Centurion Publications

The development of ultrafast gas electron diffraction with nonrelativistic electrons has enabled the determination of molecular structures with atomic spatial resolution. It has, however, been challenging to break the picosecond temporal resolution barrier and achieve the goal that has long been envisioned - making space- and-time resolved molecular movies of chemical reaction in the gas-phase. Recently, an ultrafast electron diffraction (UED) apparatus using mega-electron-volt (MeV) electrons was developed at the SLAC National Accelerator Laboratory for imaging ultrafast structural dynamics of molecules in the gas phase. The SLAC gas-phase MeV UED has achieved 65 fs root mean square temporal resolution, 0.63 …

Roadmap On Photonic, Electronic And Atomic Collision Physics: Ii. Electron And Antimatter Interactions, Stefan Schippers, Emma Sokell, Friedrich Aumayr, Hossein Sadeghpour, Kiyoshi Ueda, Igor Bray, Klaus Bartschat, Andrew Murray, Jonathan Tennyson, Alexander Dorn, Masakazu Yamazaki, Masahiko Takahashi, Nigel Mason, Oldřich Novotný, Andreas Wolf, Leon Sanche, Martin Centurion, Yasunori Yamazaki, Gaetana Laricchia, Clifford M. Surko, James Sullivan, Gleb Gribakin, Daniel Wolf Savin, Yuri Ralchenko, Ronnie Hoekstra, Gerry O'Sullivan

Martin Centurion Publications

We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap II we focus on electron and antimatter interactions. Modern theoretical and experimental approaches provide detailed insight into the many body quantum dynamics of leptonic collisions with targets of varying complexity ranging from neutral and charged atoms to large biomolecules and clusters. These developments have been driven by technological progress and by the needs of adjacent areas of science such as astrophysics, plasma physics and radiation biophysics. This Roadmap aims at looking back along the road, explaining …

Erratum: "Imaging The Three‐Dimensional Orientation And Rotational Mobility Of Fluorescent Emitters Using The Tri‐Spot Point Spread Function", Oumeng Zhang, Jin Lu, Tianben Ding, Matthew D. Lew

Electrical & Systems Engineering Publications and Presentations

In the original paper, a calibration error exists in the image-formation model used to analyze experimental images taken by our microscope, causing a bias in the orientation measurements in Figs. 2 and 3. The updated measurements are shown in Fig. E1. We have also updated the supplementary material for the original article to discuss the revised PSF model and estimation algorithms (supplementary material 2) and show the revised model and measurements (Figs. S1, S3, S7, S8, and S10–S13).

Picosecond Time-Resolved Dynamics Of Energy Transfer Between Gan And The Various Excited States Of Eu3+ Ions, Ruoqiao Wei, Brandon Mitchell, Dolf Timmerman, Tom Gregorkiewicz, Wanxin Zhu, Jun Tatebayashi, Shuhei Ichikawa, Yasufumi Fujiwara, Volkmar Dierolf

Physics & Engineering Faculty Publications

To elucidate the energy transfer and reexcitation processes in Eu-doped GaN layers that are used in recently developed, highly efficient red light-emitting diodes, a systematic series of photoluminescence and time-resolved photoluminescence (TR-PL) measurements was performed. Critical insights on how “slow” Eu processes (∼µs) can compete against fast semiconductor processes (∼ps) are revealed using TR-PL with a high temporal resolution, as it is found that the initial energy transfer from GaN to the Eu3+ ions takes place rapidly, on a timescale of <100 ps. Below band-gap resonant excitation was used to identify the states into which the energy transfer occurs. For the most efficient Eu defect complexes, this transfer dominantly occurs directly into the 5 D0 state of Eu3+. Less efficient complexes also exhibit transfer into the 5 D2 state, the emission of which can be detected using photoluminescence at low temperature, indicating the importance of the excitation pathway on device efficiency. Under high excitation intensity, reexcitation can also occur, leading to a redistribution of population into the 5 D2, 5 D1, or 5 D0 states.

Diffractive Imaging Of Dissociation And Ground-State Dynamics In A Complex Molecule, Kyle J. Wilkin, Robert M. Parrish, Jie Yang, Thomas J.A. Wolf, J. Pedro F. Nunes, Markus Guehr, Renkai Li, Xiaozhe Shen, Qiang Zheng, Xijie Wang, Todd J. Martinez, Martin Centurion

Martin Centurion Publications

We have investigated the structural dynamics in photoexcited 1,2-diiodotetrafluoroethane molecules (C₂F₄I₂) in the gas phase experimentally using ultrafast electron diffraction and theoretically using FOMO-CASCI excited-state dynamics simulations. The molecules are excited by an ultraviolet femtosecond laser pulse to a state characterized by a transition from the iodine 5p orbital to a mixed 5p||σ hole and CF₂• antibonding orbital, which results in the cleavage of one of the carbon-iodine bonds. We have observed, with sub-Angstrom resolution, the motion of the nuclear wave packet of the dissociating iodine atom followed by …

Reconfigurable Ferromagnetic Liquid Droplets, Xubo Liu, Noah Kent, Alejandro Ceballos, Robert Streubel, Yufeng Jiang, Yu Chai, Paul Y. Kim, Joe Forth, Frances Hellman, Shaowei Shi, Dong Wang, Brett A. Helms, Paul D. Ashby, Peter Fischer, Thomas P. Russell

Robert Streubel Papers

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving themagnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic …

Excitable Interplay Between Lasing Quantum Dot States, Michael Dillane, I. Dubinkin, N. Fedorov, T. Erneux, David Goulding, B. Kelleher, E.A. Viktorov

Cappa Publications

The optically injected semiconductor laser system has proven to be an excellent source of experimental nonlinear dynamics, particularly regarding the generation of excitable pulses. Typically for low-injection strengths, these pulses are the result of a small above-threshold perturbation of a stable steady state, the underlying physics is well described by the Adler phase equation, and each laser intensity pulse is accompanied by a 2π phase rotation. In this article, we show how, with a dual-state quantum dot laser, a variation of type I excitability is possible that cannot be described by the Adler model. The laser is operated so that …

Monolayer Doping Of Silicon-Germanium Alloys: A Balancing Act Between Phosphorus Incorporation And Strain Relaxation, Noel Kennedy, Ray Duffy, Gioele Mirabelli, Luke Eaton, Nikolay Petkov, Justin D. Holmes, Chris Hatem, Lee Walsh, Brenda Long

Cappa Publications

This paper presents the application of monolayer doping (MLD) to silicon-germanium (SiGe). This study was carried out for phosphorus dopants on wafers of epitaxially grown thin films of strained SiGe on silicon with varying concentrations of Ge (18%, 30%, and 60%). The challenge presented here is achieving dopant incorporation while minimizing strain relaxation. The impact of high temperature annealing on the formation of defects due to strain relaxation of these layers was qualitatively monitored by cross-sectional transmission electron microscopy and atomic force microscopy prior to choosing an anneal temperature for the MLD drive-in. Though the bulk SiGe wafers provided are …

Structure, Stability And Vibrational Properties Of Cdse Wurtzite Molecules And Nanocrystals: A Dft Study, Mudar A. Abdulsattar, Hayder M. Abduljalil, Hussein Hakim Abed

Karbala International Journal of Modern Science

Bare and hydrogen passivated CdSe wurtzite molecules and nanostructures are investigated. The investigation is performed using wurtzoid structures that represent the wurtzite structure at the molecular and nanoscale region. The results show that the energy gap of bare and hydrogen passivated CdSe molecules is higher than and converges to the experimental bulk energy gap. Vibrational analysis of wurtzoid molecules shows that the experimental longitudinal optical mode is in between bare and hydrogen passivated CdSe molecules and very near to bare molecules. The stability of wurtzoid molecules against transition to CdSe diamondoids and cuboids that represent the molecular scale of diamond …

Using Forensics To Introduce Ir Spectroscopy & Molecular Modeling, Joseph T. Golab

Faculty Publications & Research

A student activity is reported that analyzes “medical evidence” with experimental and computational methods. The lesson demonstrates benefits of solving practical problems with integrated tools.

A Brief Review Of Modern Uses Of Scattering Techniques, Daniel M. Wade, Dereth J. Drake

Georgia Journal of Science

Thomson, Rayleigh, Mie, and Raman scattering are commonly used in several disciplines in science and engineering. The techniques involve the scattering of electromagnetic radiation or particles in a sample. This paper provides a brief history for each scattering method, describes the traditional laboratory approach for implementation, and discusses current uses and variations of these four techniques.

Rotational Quenching Of Hd Induced By Collisions With H2 Molecules, Yier Wan, Nadulvalath Balakrishnan, B. H. Yang, R. C. Forrey, P. C. Stancil

Chemistry and Biochemistry Faculty Research

Rate coefficients for rotational transitions in HD induced by H2 impact for rotational levels of HD j ≤ 8 and temperatures 10 K ≤ T ≤ 5000 K are reported. The quantum mechanical close-coupling (CC) method and the coupled-states (CS) decoupling approximation are used to obtain the cross-sections employing the most recent highly accurate H2–H2 potential energy surface (PES). Our results are in good agreement with previous calculations for low-lying rotational transitions The cooling efficiency of HD compared with H2 and astrophysical applications are briefly discussed.

The Purported Square Ice In Bilayer Graphene In A Nanoscale, Monolayer Object, Tod A. Pascal, Craig P. Schwartz, Keith V. Lawler, David Prendergast

Chemistry and Biochemistry Faculty Research

The phase diagram of water is complex, and interfacial effects can stabilize unusual structures at the nanoscale. Here, we employ bond order accelerated molecular dynamics simulations to show that upon encapsulation within bilayer graphene, water can spontaneously adopt a two-dimensional (monomolecular) layer of “square ice” at ambient conditions, instead of an encapsulated water droplet. Free energy calculations show that this motif is thermodynamically stable up to diameters of approximately 15 nm due to enhanced hydrogen bonding and favorable binding to the graphene sheets. Entropic losses due to solidification and reduced graphene–graphene binding enthalpy are opposing thermodynamic forces that conspire to …