Atomic, Molecular and Optical Physics Commons^™

Distributions Of Long-Lived Radioactive Nuclei Provided By Star-Forming Environments, Marco Fatuzzo, Fred Adams

Faculty Scholarship

Radioactive nuclei play an important role in planetary evolution by providing an internal heat source, which affects planetary structure and helps facilitate plate tectonics. A minimum level of nuclear activity is thought to be necessary—but not sufficient—for planets to be habitable. Extending previous work that focused on short-lived nuclei, this paper considers the delivery of long-lived radioactive nuclei to circumstellar disks in star forming regions. Although the long-lived nuclear species are always present, their abundances can be enhanced through multiple mechanisms. Most stars form in embedded cluster environments, so that disks can be enriched directly by intercepting ejecta from supernovae …

Electron Vortices In Photoionization By Circularly Polarized Attosecond Pulses, Jean Marcel Ngoko Djiokap, S. X. Hu, L. B. Madsen, N. L. Manakov, A. V. Meremianin, Anthony F. Starace

Anthony F. Starace Publications

Single ionization of He by two oppositely circularly polarized, time-delayed attosecond pulses is shown to produce photoelectron momentum distributions in the polarization plane having helical vortex structures sensitive to the time delay between the pulses, their relative phase, and their handedness. Results are obtained by both ab initio numerical solution of the two-electron time-dependent Schrödinger equation and by a lowest-order perturbation theory analysis. The energy, bandwidth, and temporal duration of attosecond pulses are ideal for observing these vortex patterns.

Scaling Laws For High-Order-Harmonic Generation With Midinfrared Laser Pulses, M. V. Frolov, N. L. Manakov, Wei-Hao Xiong, Liang-You Peng, J. Burgdörfer, Anthony F. Starace

Anthony F. Starace Publications

We derive an analytic expression for thewavelength scaling of the high-order-harmonic generation (HHG) yield induced by midinfrared driving laser fields. It is based on a quasiclassical description of the returning electron wave packet, which is shown to be largely independent of atomic properties. The accuracy of this analytic expression is confirmed by comparison with results of numerical solutions of the time-dependent Schr¨odinger equation for wavelengths in the range of 1.4 μm ≤ λ ≤ 4 μm. We verify the wavelength scaling of the HHG yield found numerically for midinfrared laser fields in a recent paper by Le et al. [

Favorable Target Positions For Intense Laser Acceleration Of Electrons In Hydrogen-Like, Highly-Charged Ions, Liang-Wen Pi, S. X. Hu, Anthony F. Starace

Anthony F. Starace Publications

Classical relativistic Monte Carlo simulations of petawatt laser acceleration of electrons bound initially in hydrogen-like, highly-charged ions show that both the angles and energies of the laser-accelerated electrons depend on the initial ion positions with respect to the laser focus. Electrons bound in ions located after the laser focus generally acquire higher (≈GeV) energies and are ejected at smaller angles with respect to the laser beam. Our simulations assume a tightly-focused linearly-polarized laser pulse with intensity approaching 10²²W/cm². Up to fifth order corrections to the paraxial approximation of the laser field in the focal region are …

Photodetachment Of A Model Molecular System By An Elliptically Polarized Field, M. V. Frolov, N. L. Manakov, S. S. Marmo, Anthony F. Starace

Anthony F. Starace Publications

The differential cross section for one-photon molecular detachment by an elliptically polarized field is analyzed for a one-electron molecular model comprised of an electron in the field of two (generally nonequivalent) attractive zero-range potentials (ZRPs) separated by the distance R. A phenomenological parametrization of the photodetachment cross section for a fixed-in-space molecular system in terms of two scalar dynamical parameters is presented and circular dichroism effects are discussed. Analytic results for the dynamical molecular parameters within the ZRP molecular model are used to analyze interference phenomena (including two-center interference) and dichroic effects in the detached electron angular distributions and …

Rescattering Effects In Laser-Assisted Electron-Atom Bremsstrahlung, A. N. Zheltukhin, A. V. Flegel, M. V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

Rescattering effects in non-resonant spontaneous laser-assisted electron–atom bremsstrahlung (LABrS) are analyzed within the framework of time-dependent effective-range (TDER) theory. It is shown that high energy LABrS spectra exhibit rescattering plateau structures that are similar to those that are well-known in strong field laser-induced processes as well as those that have been predicted theoretically in laser-assisted collision processes. In the limit of a low-frequency laser field, an analytic description of LABrS is obtained from a rigorous quantum analysis of the exact TDER results for the LABrS amplitude. This amplitude is represented as a sum of factorized terms involving three factors, each …

Charged Particle Dynamics In The Magnetic Field Of A Long Straight Current-Carrying Wire, M. Fatuzzo, A. Prentice, T. Toepker

Faculty Scholarship

The article discusses the concept behind motion of a charged particle in a non-uniform filed of a wire carrying current. Topics discussed include possible types of motion in a current carrying field, vector analysis of velocity and magnetic field of the particle and Coupled differential equations.

Direct Observation Of Quark-Hadron Duality In The Free Neutron F2 Structure Function, I. Niculescu, G. Niculescu, W. Melnitchouk, J. Arrington, M. E. Christy, S. Kuhn

Physics Faculty Publications

Using the recently published data from the BONuS(Barely Off-shell Nucleon Structure) experiment at Jefferson Lab, which utilized a spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F₂ structure function. The data are used to reconstruct the lowest few (N = 2, 4, and 6) moments of F₂ in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark-hadron duality holds locally …

Nonlinear Dichroism In Back-To-Back Double Ionization Of He By An Intense Elliptically Polarized Few-Cycle Extreme Ultraviolet Pulse, Jean Marcel Ngoko Djiokap, N. L. Manakov, A. V. Meremianin, S. X. Hu, L. B. Madsen, Anthony F. Starace

Anthony F. Starace Publications

Control of double ionization of He by means of the polarization and carrier-envelope phase (CEP) of an intense, few-cycle extreme ultraviolet (XUV) pulse is demonstrated numerically by solving the six-dimensional two-electron, time-dependent Schrödinger equation for He interacting with an elliptically polarized XUV pulse. Guided by perturbation theory (PT), we predict the existence of a nonlinear dichroic effect (∝ I^3/2) that is sensitive to the CEP, ellipticity, peak intensity I, and temporal duration of the pulse. This dichroic effect (i.e., the difference of the two-electron angular distributions for opposite helicities of the ionizing XUV pulse) originates from interference of …

Resonant Electron-Atom Bremsstrahlung In An Intense Laser Field, A. N. Zheltukhin, A. V. Flegel, M. V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

We analyze a resonant mechanism for spontaneous laser-assisted electron bremsstrahlung (BrS) involving the resonant transition (via either laser-assisted electron-ion recombination or electron-atom attachment) into a laser-dressed intermediate quasibound state (corresponding, respectively, to either a field-free neutral atom or a negative-ion bound state) accompanied by ionization or detachment of this state by the laser field. This mechanism leads to resonant enhancement (by orders of magnitude) of the BrS spectral density for emitted photon energies corresponding to those for laser-assisted recombination or attachment. We present an accurate parametrization of the resonant BrS amplitude in terms of the amplitudes for nonresonant BrS, for …

A Numerical Assessment Of Cosmic-Ray Energy Diffusion Through Turbulent Media, M. Fatuzzo, F. Melia

Faculty Scholarship

No abstract provided.

Effects Of Turbulence On Cosmic Ray Propagation In Protostars And Young Stars, M. Fatuzzo, F. C. Adams

Faculty Scholarship

No abstract provided.

Resonant Enhancement Of The Harmonic-Generation Spectrum Of Beryllium, Jean Marcel Ngoko Djiokap, Anthony F. Starace

Anthony F. Starace Publications

The high-order harmonic-generation (HHG) spectrum of Be is investigated in the multiphoton regime by solving the full-dimensional, two-active-electron, time-dependent Schr¨odinger equation in an intense (≈10¹³ W/cm²), 30-cycle laser field. As the laser frequency ω_L varies from 1.7 to 1.8 eV (which is in the tunable range of a Ti:sapphire laser), the seventh harmonic becomes resonant sequentially with the transition between the ground state and two doubly excited autoionizing states, 2p4s(¹P) (at ω_L = 1.734 eV) and 2p5s …

Carrier-Envelope-Phase-Induced Asymmetries In Double Ionization Of Helium By An Intense Few-Cycle Xuv Pulse, Jean Marcel Ngoko Djiokap, N. L. Manakov, A. V. Meremianin, Anthony F. Starace

Anthony F. Starace Publications

The carrier-envelope-phase (CEP) dependence of electron angular distributions in double ionization of He by an arbitrarily polarized, few-cycle, intense XUV pulse is formulated using perturbation theory (PT) in the pulse amplitude. Owing to the broad pulse bandwidth, interference of first- and second-order PT amplitudes produces asymmetric angular distributions sensitive to the CEP. The PT parametrization is shown to be valid by comparing with results of solutions of the full-dimensional, two-electron time-dependent Schrödinger equation for the case of linear polarization.

Harmonic Generation Spectroscopy With A Two-Colour Laser Field Having Orthogonal Linear Polarizations, T. S. Sarantseva, M. V. Frolov, N. L. Manakov, M. Yu. Ivanov, Anthony F. Starace

Anthony F. Starace Publications

The interpretation of many high-order harmonic generation (HHG) experiments is based on the assumption that the HHG yield of an atom can be factorized into (i) a laser-dependent ‘electron wave packet’ with rather simple properties, including a nearly universal shape, and (ii) an atomic photorecombination cross section. We show that this factorization is restricted to linearly polarized laser fields and fails in two-colour laser fields with orthogonal polarizations. At the same time, we show how two-colour HHG spectroscopy using orthogonally polarized intense fundamental and relatively weak second harmonic fields makes a complete experiment possible that enables the retrieval of the …

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.

Analytic Description Of Elastic Electron-Atom Scattering In An Elliptically Polarized Laser Field, A. V. Flegel, M. V. Frolov, N. L. Manakov, Anthony F. Starace, A. N. Zheltukhin

Anthony F. Starace Publications

An analytic description of laser-assisted electron-atom scattering (LAES) in an elliptically polarized field is presented using time-dependent effective range (TDER) theory to treat both electron-laser and electron-atom interactions nonperturbatively. Closed-form formulas describing plateau features in LAES spectra are derived quantum mechanically in the low-frequency limit. These formulas provide an analytic explanation for key features of the LAES differential cross section. For the low-energy region of the LAES spectrum, our result generalizes the Kroll-Watson formula to the case of elliptic polarization. For the high-energy (rescattering) plateau in the LAES spectrum, our result generalizes prior results for a linearly polarized field valid …

Threshold Effects In Strong-Field Ionization: Energy Shifts And Rydberg Structures, Katarzyna Krajewska, Ilya I. Fabrikant, Anthony F. Starace

Anthony F. Starace Publications

The behavior of strong-field ionization rates of neutral atoms in the vicinity ofmultiphoton ionization thresholds is analyzed using formal collision theory.Our approach,which accounts nonperturbatively for effects of an intense laser field, shows that the ionization rates have a nearly constant behavior below and above each multiphoton threshold and that between such thresholds there are an apparently finite number of rapid oscillations due to resonances with laser-field-modified Rydberg states. This pattern is typical for any atomic target, as we illustrate specifically for hydrogen and neon atoms. The flat behavior of the ionization yield near multiphoton thresholds gives the appearance of an …

Study Of The Structure Of 9C Via Single Neutron Transfer, Scott T. Marley

Dissertations

This thesis describes a study of the nucleus ⁹C, produced in the single-neutron transfer reaction d(¹⁰C, t) ⁹C using a radioactive ¹⁰C beam. The structure of the neutron-deficient nucleus ⁹C is poorly known. Only a few excited states have been observed and no information exists of their single-particle characteristics. The measured ground-state magnetic dipole moment of ⁹C is anomalously small and could imply large contributions from sd-shell orbitals in the ground-state wave function. The positions of the ⁹C excited states and their single-particle properties are vital to furthering the …

Light Vs. Quantum Gravity, Irving Martinez^*

COURI Symposium Abstracts, Spring 2012

No abstract provided.

Quantitative Study Of Spin-Flip Co-Tunneling Transport In A Quantum Dot, S. Herbert, T-M. Liu, A. N. Ngo

Faculty Scholarship

No abstract provided.

Assessing The Feasibility Of Cosmic-Ray Acceleration By Magnetic Turbulence At The Magnetic Center, M. Fatuzzo, F. Melia

Faculty Scholarship

No abstract provided.

Top Quark Rapidity Distribution And Forward-Backward Asymmetry, Nikolaos Kidonakis

Faculty Articles

I present results for the top quark rapidity distribution at Large Hadron Collider and Tevatron energies, including higher-order corrections from threshold resummation. Approximate next-to-next-to-leading-order (NNLO) results are obtained by adding the NNLO soft-gluon corrections at next-to-next-to-leading-logarithm level to the exact next-to-leading-order calculation. Theoretical predictions are shown for the rapidity distribution, including the scale dependence of the distributions. The forward-backward asymmetry at the Tevatron is also calculated.

Next-To-Next-To-Leading-Order Collinear And Soft Gluon Corrections For T-Channel Single Top Quark Production, Nikolaos Kidonakis

Faculty Articles

I present the resummation of collinear and soft-gluon corrections to single top quark production in the t channel at next-to-next-to-leading logarithm accuracy using two-loop soft anomalous dimensions. The expansion of the resummed cross section yields approximate next-to-next-to-leading-order cross sections. Numerical results for t-channel single top quark (or single antitop) production at the Tevatron and the LHC are presented, including the dependence of the cross sections on the top quark mass and the uncertainties from scale variation and parton distributions. Combined results for all single top quark production channels are also given.

Electron Transmission Characteristics And The Production Of Narrow Beams Using Glass Optics, Buddhika Senarath Dassanayake

Dissertations

Transmission of electrons through an insulating single cylindrically-shaped glass capillary of microscopic dimension has been investigated. Samples made with Borosilicate glass (PYREX 7740) were subjected to bombardment of 300-1000 eV electrons. Transmitted electrons were analyzed using a parallel-plate spectrometer coupled to a channel electron multiplier.

The transmitted electron intensity was found to decrease with increasing sample tilt angle relative to the direction of the primary beam. Two regions of transmission were found: direct where there is no interaction of the beam with the inner capillary wall, and indirect where the beam does interact with the wall. The rate of transmission …

Two-Loop Soft Anomalous Dimensions For Single Top Quark Associated Production With A W- Or H-, Nikolaos Kidonakis

Faculty Articles

I present results for the two-loop soft anomalous dimensions for associated production of a single top quark with a W boson or a charged Higgs boson. The calculation uses expressions for the massive cusp anomalous dimension, which are presented in different forms, and it allows soft-gluon resummation at next-to-next-to-leading-logarithm (NNLL) accuracy. From the NNLL resummed cross section I derive approximate NNLO cross sections for bg→tW- and bg→tH- at LHC energies of 7, 10, and 14 TeV.

Positron Annihilation Ratio Spectroscopy (Psars) Applied To Positronium Formation Studies, Robert C. Slaughter

Theses and Dissertations

A Positron Annihilation of Radiation Spectrometer (PsARS) was developed and characterized. PsARS spectroscopy as well as digital Positron Annihilation Lifetime Spectroscopy (PALS) was applied to measure positronium formation on gold nanoparticles deposited through an evaporative method onto a thin capillary tube. This gold coated capillary tube was designed to be used for positronium lifetime studies in local electric field experiments. High local electric fields can polarize a positron-electron pair, which may result in an extended lifetime of the positron. These fields may be created through the interaction of an external electric field with silver nanoparticles deposited onto the surface of …

Theoretical Top Quark Cross Section At The Fermilab Tevatron And The Cern Lhc, Nikolaos Kidonakis, Ramona Vogt

Faculty Articles

We present results for the top quark pair cross section at the Tevatron and the LHC. We use the resummed double differential cross section, employing the fully kinematics-dependent soft-anomalous-dimension matrices, to calculate the soft-gluon contributions at next-to-next-to-leading order (NNLO). We improve and update our previous estimates by refining our methods, including further subleading terms, and employing the most recent parton distribution function sets. The NNLO soft corrections significantly enhance the NLO cross section while considerably reducing the scale dependence. We provide a detailed discussion of all theoretical uncertainties in our calculation, including kinematics, scale, and parton distribution uncertainties, and clarify …

Higgs Production Via B Bbar -> H In Hadron Colliders, Nikolaos Kidonakis

Faculty Articles

I present NNNLO collinear and soft gluon corrections for Higgs production via the process b bbar -> H. I show that the collinear corrections dominate and contribute large enhancements to the cross section at both the Tevatron and the LHC.

Status Of Eikonal Two-Loop Calculations With Massive Quarks, Nikolaos Kidonakis, Philip Stephens

Faculty Articles

We present results for two-loop diagrams with massive quarks in the eikonal approximation. Explicit expressions are given for the UV poles in dimensional regularization of several of the required integrals.