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Physics Faculty Research & Creative Works

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Articles 751 - 780 of 1762

Full-Text Articles in Physical Sciences and Mathematics

Accurate Retrieval Of Target Structures And Laser Parameters Of Few-Cycle Pulses From Photoelectron Momentum Spectra, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, J. Rauschenberger, M. F. Kling, C. D. Lin Feb 2009

Accurate Retrieval Of Target Structures And Laser Parameters Of Few-Cycle Pulses From Photoelectron Momentum Spectra, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, J. Rauschenberger, M. F. Kling, C. D. Lin

Physics Faculty Research & Creative Works

We illustrate a new method of analyzing three-dimensional momentum images of high-energy photoelectrons generated by intense phase-stabilized few-cycle laser pulses. Using photoelectron momentum spectra that were obtained by velocity-map imaging of above-threshold ionization of xenon and argon targets, we show that the absolute carrier-envelope phase, the laser peak intensity, and pulse duration can be accurately determined simultaneously (with an error of a few percent). We also show that the target structure, in the form of electron-target ion elastic differential cross sections, can be retrieved over a range of energies. The latter offers the promise of using laser-generated electron spectra for …

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Recursive Algorithm For Arrays Of Generalized Bessel Functions: Numerical Access To Dirac-Volkov Solutions, Erik Lötstedt, Ulrich D. Jentschura Feb 2009

Recursive Algorithm For Arrays Of Generalized Bessel Functions: Numerical Access To Dirac-Volkov Solutions, Erik Lötstedt, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

In the relativistic and the nonrelativistic theoretical treatment of moderate and high-power laser-matter interaction, the generalized Bessel function occurs naturally when a Schrödinger-Volkov and Dirac-Volkov solution is expanded into plane waves. For the evaluation of cross sections of quantum electrodynamic processes in a linearly polarized laser field, it is often necessary to evaluate large arrays of generalized Bessel functions, of arbitrary index but with fixed arguments. We show that the generalized Bessel function can be evaluated, in a numerically stable way, by utilizing a recurrence relation and a normalization condition only, without having to compute any initial value. We demonstrate …

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The Search For Quantum Critical Scaling In A Classical System, Jagat Lamsal, John Gaddy, Marcus Petrovic, Wouter Montfrooij, Thomas Vojta Jan 2009

The Search For Quantum Critical Scaling In A Classical System, Jagat Lamsal, John Gaddy, Marcus Petrovic, Wouter Montfrooij, Thomas Vojta

Physics Faculty Research & Creative Works

Order-disorder phase transitions in magnetic metals that occur at zero temperature have been studied in great detail. Theorists have advanced scenarios for these quantum critical systems in which the unusual response can be seen to evolve from a competition between ordering and disordering tendencies, driven by quantum fluctuations. Unfortunately, there is a potential disconnect between the real systems that are being studied experimentally, and the idealized systems that theoretical scenarios are based upon. Here we discuss how disorder introduces a change in morphology from a three-dimensional system to a collection of magnetic clusters, and we present neutron scattering data on …

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Kinetic Energy Release Distributions For C⁺₂ Emission From Multiply Charged C₆₀ And C₇₀ Fullerenes, Henrik Cederquist, Nicole Haag, Zoltan Berenyi, Peter Reinhed, Daniel Fischer, M. Gudmundsson, Birgitta W. Johansson, Torsten Schmidt, Henning Zettergren Jan 2009

Kinetic Energy Release Distributions For C⁺₂ Emission From Multiply Charged C₆₀ And C₇₀ Fullerenes, Henrik Cederquist, Nicole Haag, Zoltan Berenyi, Peter Reinhed, Daniel Fischer, M. Gudmundsson, Birgitta W. Johansson, Torsten Schmidt, Henning Zettergren

Physics Faculty Research & Creative Works

We present asystematic study of experimental kinetic energy release distributions for the asymmetric fission processes Cq+60 C(iq-1<)+70+ C+2 and C q+70 C(q-1)+60+ C+ 2 for mother ions incharge states q 4-8 produced incollisions with slow highly charged ions. Somewhat to our surprise, we find that the KERD for asymmetric fission from Cq+60 are considerably wider and have larger most likely values than the Cq+70 distributions inthe corresponding charge states when q > 4.

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Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin Jan 2009

Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

Laser-induced electron recollisions are fundamental to many strong field phenomena in atoms and molecules. Using the recently developed quantitative rescattering theory, we demonstrate that the nonsequential double ionization (NSDI) of atoms by lasers can be obtained quantitatively in terms of inelastic collisions of the target ions with the free returning electrons where the latter are explicitly given by a spectrum-characterized wave packet. Using argon atoms as target, we calculated the NSDI yield including contributions from direct (e,2e) electron-impact ionization and electron-impact excitation accompanied by subsequent field ionization. We further investigate the dependence of total NSDI on the carrier-envelope phase of …

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Electron Angular Distributions In He Single Ionization Impact By H₂⁺ Ions At 1 Mev, Shaofeng Zhang, J. Suske, Daniel Fischer, K. U. Kuehnel, Siegbert Hagmann, Alexander B. Voitkiv, B. Najjari, Achim Krauss, Robert Moshammer, Joachim Hermann Ullrich, Xinwen Ma Jan 2009

Electron Angular Distributions In He Single Ionization Impact By H₂⁺ Ions At 1 Mev, Shaofeng Zhang, J. Suske, Daniel Fischer, K. U. Kuehnel, Siegbert Hagmann, Alexander B. Voitkiv, B. Najjari, Achim Krauss, Robert Moshammer, Joachim Hermann Ullrich, Xinwen Ma

Physics Faculty Research & Creative Works

For the first time we investigated in a kinematically complete experiment the ionization of helium in collisions with H2+-molecular ions at 1 MeV. Using two separate detectors, the orientation of the projectile H2+-molecular ions was determined at the instance of the collision. The electron angular distribution was measured by a "Reaction Microscope". The observed structures are found in agreement with theoretical calculations, indicating that the ionized electron of He shows a slight preferential emission direction parallel to the molecular axis.

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Sequential And Direct Two-Photon Double Ionization Of D₂ At Flash, Y. H. Jiang, Artem Rudenko, Kai Uwe Kuhnel, Th. Ergler, S. Ludemann, Karl Zrost, Daniel Fischer, J. Perez-Torres, E. Plesiat, F. Martin, L. Foucar, J. Titze, Markus S. Schoffler, Reinhard Dorner, J. L. Sanz-Vicario, S. Dusterer, R. Treusch, Claus Dieter Schroter, Robert Moshammer, Joachim Hermann Ullrich Jan 2009

Sequential And Direct Two-Photon Double Ionization Of D₂ At Flash, Y. H. Jiang, Artem Rudenko, Kai Uwe Kuhnel, Th. Ergler, S. Ludemann, Karl Zrost, Daniel Fischer, J. Perez-Torres, E. Plesiat, F. Martin, L. Foucar, J. Titze, Markus S. Schoffler, Reinhard Dorner, J. L. Sanz-Vicario, S. Dusterer, R. Treusch, Claus Dieter Schroter, Robert Moshammer, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Sequential and direct two-photon double ionization (DI) of D2 molecule is studied experimentally and theoretically at a photon energy of 38.8 eV. Experimental and theoretical kinetic energy releases of D++D+fragments, consisting of the contributions of sequential DI via the D2+(1sσg) state and direct DI via a virtual state, agree well with each other.

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Isotope Shifts In Dielectronic Recombination: From Stable To In-Flight-Produced Nuclei, Carsten Brandau, S. Kozhedub, Alfred K. Muller, Dietrich Bernhardt, Stefan Bohm, Fritz J. Bosch, Daniel Boutin, Fred John Currell, Christina Dimopoulou, Bernhard Franzke, Alexandre Gumberidze, Zoltan Harman, Ulrich D. Jentschura, Christoph H. Keitel, Heinz Jurgen Kluge, S. Kozhedub, Reiner Krucken, Yu A. Litvinov, Fritz Nolden, Brian E. O'Rourke, Regina Reuschl, Stefan Schippers, Vladimir M. Shabaev, Uwe Spillmann, Zbigniew Stachura Jan 2009

Isotope Shifts In Dielectronic Recombination: From Stable To In-Flight-Produced Nuclei, Carsten Brandau, S. Kozhedub, Alfred K. Muller, Dietrich Bernhardt, Stefan Bohm, Fritz J. Bosch, Daniel Boutin, Fred John Currell, Christina Dimopoulou, Bernhard Franzke, Alexandre Gumberidze, Zoltan Harman, Ulrich D. Jentschura, Christoph H. Keitel, Heinz Jurgen Kluge, S. Kozhedub, Reiner Krucken, Yu A. Litvinov, Fritz Nolden, Brian E. O'Rourke, Regina Reuschl, Stefan Schippers, Vladimir M. Shabaev, Uwe Spillmann, Zbigniew Stachura

Physics Faculty Research & Creative Works

The study of isotope shifts and hyperfine effects in dielectronic recombination (DR) resonance spectra strikes a conceptually new path for investigations of nuclear properties such as charge radius, spin, magnetic moment of nuclei or lifetimes of long-lived excited nuclear states. A series of DR experiments with heavy three-electron ions (Li-like) was performed at the heavy-ion storage ring ESR of the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. In a pilot experiment the two stable isotopes A=142 and A=150 of neodymium ANd57+ were investigated. From the displacement of DR resonances the isotope shifts δE142,150(2s - 2Pl/2) …

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Unified Treatment Of Even And Odd Anharmonic Oscillators Of Arbitrary Degree, Ulrich D. Jentschura, Andrey Surzhykov, Jean Zinn-Justin Jan 2009

Unified Treatment Of Even And Odd Anharmonic Oscillators Of Arbitrary Degree, Ulrich D. Jentschura, Andrey Surzhykov, Jean Zinn-Justin

Physics Faculty Research & Creative Works

We present a unified treatment, including higher-order corrections, of anharmonic oscillators of arbitrary even and odd degree. Our approach is based on a dispersion relation which takes advantage of the [script P][script T] symmetry of odd potentials for imaginary coupling parameter, and of generalized quantization conditions which take into account instanton contributions. We find a number of explicit new results, including the general behavior of large-order perturbation theory for arbitrary levels of odd anharmonic oscillators, and subleading corrections to the decay width of excited states for odd potentials, which are numerically significant.

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Emission Of Low-Energy Photons By Electrons At Electron-Positron And Electron-Ion Colliders With Dense Bunches, Ulrich D. Jentschura, G. L. Kotkin, V. G. Serbo Jan 2009

Emission Of Low-Energy Photons By Electrons At Electron-Positron And Electron-Ion Colliders With Dense Bunches, Ulrich D. Jentschura, G. L. Kotkin, V. G. Serbo

Physics Faculty Research & Creative Works

Usually, the emission of low-energy photons in electron-positron (or electron-ion) bunch collisions is calculated with the same approach as for synchrotron radiation (beamstrahlung). However, for soft photons (Eγ

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Coulomb-Field-Induced Conversion Of A High-Energy Photon Into A Pair Assisted By A Counterpropagating Laser Beam, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel Jan 2009

Coulomb-Field-Induced Conversion Of A High-Energy Photon Into A Pair Assisted By A Counterpropagating Laser Beam, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

The laser-induced modification of a fundamental process of quantum electrodynamics, the conversion of a high-energy gamma photon in the Coulomb field of a nucleus into an electron-positron pair, is studied theoretically. Although the employed formalism allows for the general case where the gamma photon and laser photons cross at an arbitrary angle, we here focus on a theoretically interesting and numerically challenging setup, where the laser beam and gamma photon counterpropagate and impinge on a nucleus at rest. For a peak laser field smaller than the critical Schwinger field and gamma photon energy larger than the field-free threshold, the total …

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Infinite-Randomness Quantum Critical Points Induced By Dissipation, Thomas Vojta, Chetan Kotabage, Jose A. Hoyos Jan 2009

Infinite-Randomness Quantum Critical Points Induced By Dissipation, Thomas Vojta, Chetan Kotabage, Jose A. Hoyos

Physics Faculty Research & Creative Works

We develop a strong-disorder renormalization group to study quantum phase transitions with continuous O(N) symmetry order parameters under the influence of both quenched disorder and dissipation. For Ohmic dissipation, as realized in Hertz's theory of the itinerant antiferromagnetic transition or in the superconductor-metal transition in nanowires, we find the transition to be governed by an exotic infinite-randomness fixed point in the same universality class as the (dissipationless) random transverse-field Ising model. We determine the critical behavior and calculate key observables at the transition and in the associated quantum Griffiths phase. We also briefly discuss the cases of super-Ohmic and sub-Ohmic …

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Extensions Of Effective-Medium Theory Of Transport In Disordered Systems, V. M. Kenkre, Z. Kalay, Paul Ernest Parris Jan 2009

Extensions Of Effective-Medium Theory Of Transport In Disordered Systems, V. M. Kenkre, Z. Kalay, Paul Ernest Parris

Physics Faculty Research & Creative Works

The effective-medium theory of transport in disordered systems, whose basis is the replacement of spatial disorder by temporal memory, is extended in several practical directions. Restricting attention to a one-dimensional system with bond disorder for specificity, a transformation procedure is developed to deduce explicit expressions for the memory functions from given distribution functions characterizing the system disorder. It is shown how to use the memory functions in the Laplace domain forms in which they first appear, and in the time domain forms which are obtained via numerical inversion algorithms, to address time evolution of the system beyond the asymptotic domain …

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Infinite-Randomness Critical Point In The Two-Dimensional Disordered Contact Process, Thomas Vojta, A. Farquhar, J. Mast Jan 2009

Infinite-Randomness Critical Point In The Two-Dimensional Disordered Contact Process, Thomas Vojta, A. Farquhar, J. Mast

Physics Faculty Research & Creative Works

We study the nonequilibrium phase transition in the two-dimensional contact process on a randomly diluted lattice by means of large-scale Monte Carlo simulations for times up to 1010 and system sizes up to 8000×8000 sites. Our data provide strong evidence for the transition being controlled by an exotic infinite-randomness critical point with activated (exponential) dynamical scaling. We calculate the critical exponents of the transition and find them to be universal, i.e., independent of disorder strength. The Griffiths region between the clean and the dirty critical points exhibits power-law dynamical scaling with continuously varying exponents. We discuss the generality of our …

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Interference Effects Due To Projectile Target Nucleus Scattering In Single Ionization Of H₂ By 75-Kev Proton Impact, Jason S. Alexander, Aaron C. Laforge, Ahmad Hasan, Z. S. Machavariani, M. F. Ciappina, R. D. Rivarola, Don H. Madison, Michael Schulz Dec 2008

Interference Effects Due To Projectile Target Nucleus Scattering In Single Ionization Of H₂ By 75-Kev Proton Impact, Jason S. Alexander, Aaron C. Laforge, Ahmad Hasan, Z. S. Machavariani, M. F. Ciappina, R. D. Rivarola, Don H. Madison, Michael Schulz

Physics Faculty Research & Creative Works

Doubly differential cross sections (DDCSs) for single ionization of molecular hydrogen by 75-keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. Interference structures are observed in the scattering angular dependence of the DDCSs, which disappear, however, at electron speeds near the projectile speed. The comparison to our calculations shows that the projectile-target nucleus interaction plays a central role. Furthermore, our data suggest that for a given scattering angle, ionization favors well-defined molecular orientations.

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Spin- And Fine-Structure-Resolved Ionization Of Krypton, S. Bellm, J. Lower, R. P. Mceachran, E. Weigold, Ciarán Ryan-Anderson, Don H. Madison Dec 2008

Spin- And Fine-Structure-Resolved Ionization Of Krypton, S. Bellm, J. Lower, R. P. Mceachran, E. Weigold, Ciarán Ryan-Anderson, Don H. Madison

Physics Faculty Research & Creative Works

The influence of exchange, correlation, and relativistic effects in the ionization of heavy-target atoms can be sensitively probed by kinematically complete studies involving spin-polarized electrons, in particular when the fine structure of the residual ion is resolved. We present spin asymmetries, triple differential cross sections, and branching ratios for the ionization, by 127.5-eV and 114.3-eV electrons, of ground-state krypton atoms leading to the Kr+ 4s 2S1/2, 4p5 2P1/2, and 4p5 2P3/2 states. In order to untangle contributions from different physical effects, the experimental results are compared to those from distorted-wave Born approximation calculations (non- and semirelativistic) in which bound-state and …

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Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison Dec 2008

Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison

Physics Faculty Research & Creative Works

A nonperturbative close-coupling technique is used to calculate differential cross sections for the electron-impact ionization of H2 at an energy of 35.4 eV. Our approach allows cross sections for any orientation of the molecule with respect to the incident electron beam to be analyzed. New features in the resulting cross sections are found compared with the case where the molecular orientation is averaged, and also with cross sections for He at equivalent electron kinematics. When averaged over all possible molecular orientations, good agreement is found with recent experimental results.

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Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai Dec 2008

Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai

Physics Faculty Research & Creative Works

We observe high-order harmonic spectra generated from a thin atomic medium, Ar, Kr, and Xe, by intense 800-nm and 1300-nm femtosecond pulses. A clear signature of a single-atom response is observed in the harmonic spectra. Especially in the case of Ar, a Cooper minimum, reflecting the electronic structure of the atom, is observed in the harmonic spectra. We successfully extract the photorecombination cross sections of the atoms in the field-free condition with the help of an accurate recolliding electron wave packet. The present protocol paves the way for exploring ultrafast imaging of molecular dynamics with attosecond resolution.

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Built-In Electric Field Assisted Spin Injection In Cr And Mn Δ-Layer Doped Aln/Gan(0001) Heterostructures From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman Dec 2008

Built-In Electric Field Assisted Spin Injection In Cr And Mn Δ-Layer Doped Aln/Gan(0001) Heterostructures From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman

Physics Faculty Research & Creative Works

Highly spin-polarized diluted ferromagnetic semiconductors are expected to be widely used as ideal spin injectors. Here, extensive first-principles density-functional theory calculations have been performed to investigate the feasibility of using Cr- and Mn-doped wurtzite polar AlN/GaN(0001) heterostructures, with the aim to realize the appealing half-metallic character and, hence, efficient electrical spin injection. To overcome the formation of detrimental embedded clusters, we propose digital delta-layer doping perpendicular to the growth direction so as to realize enhanced performance at room temperature. The formation energy, electronic and magnetic properties, and the degree of spin polarization for both neutral and charged valence states for …

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New (E,2e) Studies Of Atomic And Molecular Targets, E. M. Staicu-Casagrande, A. Naja, A. Lahmam-Bennani, A. S. Kheifets, Don H. Madison, B. Joulakian Nov 2008

New (E,2e) Studies Of Atomic And Molecular Targets, E. M. Staicu-Casagrande, A. Naja, A. Lahmam-Bennani, A. S. Kheifets, Don H. Madison, B. Joulakian

Physics Faculty Research & Creative Works

We report new coplanar (e,2e) measurements characterised by large energy transfer and close to minimum momentum transfer from the projectile to the target. Ionisation of the two-electron targets He and H2 is investigated under these particular kinematics. The experimental data are compared with the predictions of the most elaborate theoretical models. The obtained good agreement motivated us to extend our research to the case of more complex targets such as Ar. Comparison with the most elaborate models in the case of multi-electron targets is excellent. Destructive and constructive interference effects in the case of H2 are observed and …

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Laser Channeling Of Bethe-Heitler Pairs, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel Nov 2008

Laser Channeling Of Bethe-Heitler Pairs, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

Electron-positron pair creation is analyzed for an arrangement involving three external fields: a high-frequency gamma photon, the Coulomb field of a nucleus, and a strong laser wave. The frequency of the incoming gamma photon is assumed to be larger than the threshold for pair production in the absence of a laser, and the peak electric field of the laser is assumed to be much weaker than Schwinger's critical field. The total number of pairs produced is found to be essentially unchanged by the laser field, while the differential cross section is drastically modified. We show that the laser can channel …

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Revisiting Unitarity Corrections For Electromagnetic Processes In Collisions Of Relativistic Nuclei, Ulrich D. Jentschura, Kai Hencken, Valery G. Serbo Nov 2008

Revisiting Unitarity Corrections For Electromagnetic Processes In Collisions Of Relativistic Nuclei, Ulrich D. Jentschura, Kai Hencken, Valery G. Serbo

Physics Faculty Research & Creative Works

Unitarity corrections to several electromagnetic processes in collisions of relativistic heavy nuclei are considered. They are due to the unitarity requirement for the S-matrix and correspond to the exchange of a light-by-light scattering block between colliding nuclei. We obtain improved results for the corrections to e+ e- and μ+ μ- pair production as well as new results for unitarity corrections to the production of photons via virtual Compton and virtual Delbrück scattering. These corrections can be numerically large; e.g., the μ+ μ- pair production cross section is reduced by about 50% and nuclear bremsstrahlung …

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Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas Oct 2008

Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas

Physics Faculty Research & Creative Works

We investigate blackbody-induced energy shifts for low-lying levels of atomic systems, with a special emphasis on transitions used in current and planned high-precision experiments on atomic hydrogen and ionized helium. Fine-structure- and Lamb-shift-induced blackbody shifts are found to increase with the square of the nuclear charge number, whereas blackbody shifts due to virtual transitions decrease with increasing nuclear charge as the fourth power of the nuclear charge. We also investigate the decay width acquired by the ground state of atomic hydrogen, due to interaction with blackbody photons. The corresponding width is due to an instability against excitation to higher excited …

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Simulations Of Baryon Acoustic Oscillations - I. Growth Of Large-Scale Density Fluctuations, Ryuichi Takahashi, Naoki Yoshida, Shun Saito, For Full List Of Authors, See Publisher's Website. Oct 2008

Simulations Of Baryon Acoustic Oscillations - I. Growth Of Large-Scale Density Fluctuations, Ryuichi Takahashi, Naoki Yoshida, Shun Saito, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We critically examine how well the evolution of large-scale density perturbations is followed in cosmological N-body simulations. We first run a large volume simulation and perform a mode-by-mode analysis in three-dimensional Fourier space. We show that the growth of large-scale fluctuations significantly deviates from linear-theory predictions. The deviations are caused by non-linear coupling with a small number of modes at largest scales owing to finiteness of the simulation volume. We then develop an analytic model based on second-order perturbation theory to quantify the effect. Our model accurately reproduces the simulation results. For a single realization, the second-order effect appears typically …

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Absolute Cross Sections For The Ionization-Excitation Of Helium By Electron Impact, S. Bellm, J. Lower, E. Weigold, I. Bray, D. V. Fursa, K. Bartschat, Don H. Madison, Allison L. Harris Sep 2008

Absolute Cross Sections For The Ionization-Excitation Of Helium By Electron Impact, S. Bellm, J. Lower, E. Weigold, I. Bray, D. V. Fursa, K. Bartschat, Don H. Madison, Allison L. Harris

Physics Faculty Research & Creative Works

In a recent publication we presented detailed experimental and theoretical results for the electron-impact-induced ionization of ground-state helium atoms. The purpose of that work was to refine theoretical approaches and provide further insight into the Coulomb four-body problem. Cross section ratios were presented for transitions leading to excited states, relative to those leading to the ground state, of the helium ion. We now build on that study by presenting individual relative triple-differential ionization cross sections (TDCSs) for an additional body of experimental data measured at lower values of scattered-electron energies. This has been facilitated through the development of new electron-gun …

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Ergoregion Instability Of Black Hole Mimickers, Paolo Pani, Vitor Cardoso, Mariano Cadoni, Marco Cavaglia Aug 2008

Ergoregion Instability Of Black Hole Mimickers, Paolo Pani, Vitor Cardoso, Mariano Cadoni, Marco Cavaglia

Physics Faculty Research & Creative Works

Ultra-compact, horizonless objects such as gravastars, boson stars, wormholes and superspinars can mimick most of the properties of black holes. Here we show that these "black hole mimickers" will most likely develop a strong ergoregion instability when rapidly spinning. Instability timescales range between ∼ 10-5s and ∼ weeks depending on the object, its mass and its angular momentum. For a wide range of parameters the instability is truly effective. This provides a strong indication that astrophysical ultra-compact objects with large rotation are black holes.

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Extraction Of The Species-Dependent Dipole Amplitude And Phase From High-Order Harmonic Spectra In Rare-Gas Atoms, Anh-Thu Le, Toru Morishita, C. D. Lin Aug 2008

Extraction Of The Species-Dependent Dipole Amplitude And Phase From High-Order Harmonic Spectra In Rare-Gas Atoms, Anh-Thu Le, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

Based on high-order harmonic generation (HHG) spectra obtained from solving the time-dependent Schrödinger equation for atoms, we established quantitatively that the HHG yield can be expressed as the product of a returning electron wave packet and photorecombination cross sections, and the shape of the returning wave packet is shown to be largely independent of the species. By comparing the HHG spectra generated from different targets under identical laser pulses, accurate structural information, including the phase of the recombination amplitude, can be retrieved. This result opens up the possibility of studying the target structure of complex systems, including their time evolution, …

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Evidence Of Wave-Particle Duality For Single Fast Hydrogen Atoms, Henning T. Schmidt, Daniel Fischer, Zoltan Berenyi, C. Lewis Cocke, M. Gudmundsson, Nicole Haag, Henrik A B Johansson, Anders Kallberg, Sergey B. Levin, Peter Reinhed, Ulf Sassenberg, Reinhold S. Schuch, Ansgar Simonsson, Kristian Stochkel, Henrik Cederquist Aug 2008

Evidence Of Wave-Particle Duality For Single Fast Hydrogen Atoms, Henning T. Schmidt, Daniel Fischer, Zoltan Berenyi, C. Lewis Cocke, M. Gudmundsson, Nicole Haag, Henrik A B Johansson, Anders Kallberg, Sergey B. Levin, Peter Reinhed, Ulf Sassenberg, Reinhold S. Schuch, Ansgar Simonsson, Kristian Stochkel, Henrik Cederquist

Physics Faculty Research & Creative Works

We report the direct observation of interference effects in a Young's double-slit experiment where the interfering waves are two spatially separated components of the de Broglie wave of single 1.3 MeV hydrogen atoms formed close to either target nucleus in H++H2 electron-transfer collisions. Quantum interference strongly influences the results even though the hydrogen atoms have a de Broglie wavelength, λdB, as small as 25 fm.

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Signature Of Ericson Fluctuations In Helium Inelastic Scattering Cross Sections Near The Double Ionization Threshold, Junliang Xu, Anh-Thu Le, Toru Morishita, C. D. Lin Jul 2008

Signature Of Ericson Fluctuations In Helium Inelastic Scattering Cross Sections Near The Double Ionization Threshold, Junliang Xu, Anh-Thu Le, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

We calculated the inelastic electron impact excitation cross sections of He⁺ by electrons for a model helium atom to examine the onset of the signature of quantum chaotic scattering in this simple system. We find Ericson fluctuations (EF) in the calculated inelastic scattering cross sections only when the impact energies lie within about 0.21 eV below the double ionization threshold. We also discuss the stringent requirements and the proper methods for analyzing the inelastic scattering cross sections in order to observe EF experimentally.

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Relation Between Channel And Spatial Mesoscopic Correlations In Volume-Disordered Waveguides, Alexey Yamilov Jul 2008

Relation Between Channel And Spatial Mesoscopic Correlations In Volume-Disordered Waveguides, Alexey Yamilov

Physics Faculty Research & Creative Works

We investigate the relationship between channel and spatial mesoscopic correlations in volume-disordered waveguides. We emphasize the importance of the surface escape function, which describes the distribution of transmitted flux among different channels, and we derive expressions for spatial field and intensity correlation functions directly from the channel ones.

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