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403 full-text articles. Page 1 of 11.

Imaging Population Transfer In Atoms With Ultrafast Electron Pulses, Hua-Chieh Shao, Anthony F. Starace 2016 Purdue University

Imaging Population Transfer In Atoms With Ultrafast Electron Pulses, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

We propose the use of ultrafast electron diffraction (UED) to image a controllable, laser-driven coherent electron population transfer in lithium atoms with currently available femtosecond electron pulses. Our simulations demonstrate the ability of ultrafast electrons to image such an electronic population transfer, thus validating UED as a direct means of investigating electron dynamics. Provided the incident electron pulses have sufficient temporal resolution, the diffraction images are shown to resolve also the relative phases of the target electronic wave functions.


High-Flux Femtosecond X-Ray Emission From Controlled Generation Of Annular Electron Beams In A Laser Wakefield Accelerator, T. Z. Zhao, K. Behm, C. F. Dong, X. Davoine, Serge Y. Kalmykov, V. Petrov, Vladimir Chvykov, P. Cummings, B. Hou, Anatoly Maksimchuk, J. A. Nees, Victor Yanovsky, A. G. R. Thomas, Karl Krushelnick 2016 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109

High-Flux Femtosecond X-Ray Emission From Controlled Generation Of Annular Electron Beams In A Laser Wakefield Accelerator, T. Z. Zhao, K. Behm, C. F. Dong, X. Davoine, Serge Y. Kalmykov, V. Petrov, Vladimir Chvykov, P. Cummings, B. Hou, Anatoly Maksimchuk, J. A. Nees, Victor Yanovsky, A. G. R. Thomas, Karl Krushelnick

Serge Youri Kalmykov

Annular quasimonoenergetic electron beams with a mean energy in the range 200–400 MeV and charge on the order of several picocoulombs were generated in a laser wakefield accelerator and subsequently accelerated using a plasma afterburner in a two-stage gas cell. Generation of these beams is associated with injection occurring on the density down ramp between the stages. This well-localized injection produces a bunch of electrons performing coherent betatron oscillations in the wakefield, resulting in a significant increase in the x-ray yield. Annular electron distributions are detected in 40% of shots under optimal conditions. Simultaneous control of the pulse duration ...


Multistart Spiral Electron Vortices In Ionization By Circularly Polarized Uv Pulses, Jean Marcel Ngoko Djiokap, Alexei V. Meremianin, N. L. Manakov, S. X. Hu, L. B. Madsen, Anthony F. Starace 2016 University of Nebraska-Lincoln

Multistart Spiral Electron Vortices In Ionization By Circularly Polarized Uv Pulses, Jean Marcel Ngoko Djiokap, Alexei V. Meremianin, N. L. Manakov, S. X. Hu, L. B. Madsen, Anthony F. Starace

Anthony F. Starace Publications

Multistart spiral vortex patterns are predicted for the electron momentum distributions in the polarization plane following ionization of the helium atom by two time-delayed circularly polarized ultrashort laser pulses. For two ultraviolet (UV) pulses having the same frequency (such that two photons are required for ionization), single-color two-photon interferometry with corotating or counter-rotating time-delayed pulses is found to lead respectively to zero-start or four-start spiral vortex patterns in the ionized electron momentum distributions in the polarization plane. In contrast, two-color one-photon plus two-photon interferometry with time-delayed corotating or counter-rotating UV pulses is found to lead respectively to one ...


Power And Langmuir Probe Measurements Of H2 Rf Plasma, Alexander A. Stowell 2016 Macalester College

Power And Langmuir Probe Measurements Of H2 Rf Plasma, Alexander A. Stowell

Macalester Journal of Physics and Astronomy

Methane based gases are often used to produce thin films of biomaterials, such as diamond-like carbon, through Plasma Enhanced Chemical Vapor Deposition. The characterization of the H2 plasma will give a deeper understanding of the physical processes occurring. Understanding these processes could lead to the optimization of the production of these thin films in the future. In this paper, we examine the H2 plasma using a Langmuir probe to gain information on the electron temperature and density of the plasma discharge. We measured electron temperatures of 6eV. Our Langmuir probe data indicates the electron temperature remains constant as ...


Dissociative Excitation Of H2 In An Rf Plasma, John Carlson 2016 Macalester College

Dissociative Excitation Of H2 In An Rf Plasma, John Carlson

Macalester Journal of Physics and Astronomy

Plasma-enhanced chemical vapor deposition is a widely used method for depositing thin films. In order to optimize the properties of the films, it is important to understand the plasma processes that occur during film growth. In this research we use optical emission spectroscopy in order to measure the spectral emission lines of a plasma produced with hydrogen gas. In conjunction with other measurements and modeling, these measurements can provide insight to the electron energy distribution of the plasma.


Spontaneous Parametric Down Conversion Of Photons Through Β-Barium Borate, Luke Horowitz 2016 California Polytechnic State University, San Luis Obispo

Spontaneous Parametric Down Conversion Of Photons Through Β-Barium Borate, Luke Horowitz

Physics

An apparatus for detecting pairs of entangled 405nm photons that have undergone Spontaneous Parametric Down Conversion through β-Barium Borate is described. By using avalanche photo-diodes to detect the low-intensity converted beam and a coincidence module to register coincident photons, it is possible to create an apparatus than can be used to perform quantum information experiments under a budget appropriate for an undergraduate physics lab.


Modeling The Sps Feedback And Feedforward Systems For Improved Performance, Jake Hargrove 2016 California Polytechnic State University, San Luis Obispo

Modeling The Sps Feedback And Feedforward Systems For Improved Performance, Jake Hargrove

Physics

The Super Proton Synchrotron (SPS) is the last link in the chain of accelerators providing protons to the Large Hadron Collider (LHC). The SPS is currently the limiting factor on the maximum number of protons and thus collisions in the LHC. The SPS upgrade is under way to expand the discovery potential of the LHC. The accelerating system — Radio Frequency (RF) — is being improved. Models of the SPS RF feedback systems were developed. These models could assist with design choices, evaluating the upgraded system performance, and anticipate limitations and issues.


Investigation Of Langmuir Probes In Non-Maxwellian Plasma Using Particle-In-Cell (Pic) Modeling, Densu Aktas Lister 2016 University of Tennessee - Knoxville

Investigation Of Langmuir Probes In Non-Maxwellian Plasma Using Particle-In-Cell (Pic) Modeling, Densu Aktas Lister

Doctoral Dissertations

This dissertation explores the development of a capability for simulating the plasma dynamics of Langmuir probes (LP) in complex plasmas where the velocity distributions are non-equilibrium and the electron energy spectrum is non-Maxwellian with respect to laboratory and space experiments. The results of this investigation are interpreted to give recommendations for design and use of LPs. This work is conducted using computational techniques to create the exact plasma conditions of the experimental testing environments. The investigations address the following topics:

  • development of a technique to model non-Maxwellian physics,
  • modification of a baseline-technique and optimization of it for this application,
  • creation ...


Diffractive Imaging Of A Rotational Wavepacket In Nitrogen Molecules With Femtosecond Megaelectronvolt Electron Pulses, Jie Yang, Markus Guehr, Theodore Vecchione, Matthew S. Robinson, Renkai Li, Nick Hartmann, Xiaozhe Shen, Ryan Coffee, Jeff Corbett, Alan Fry, Kelly Gaffney, Tais Gorkhover, Carsten Hast, Keith Jobe, Igor Makasyuk, Alexander Reid, Joseph Robinson, Sharon Vetter, Fenglin Wang, Stephen Weathersby, Charles Yoneda, Martin Centurion, Xijie Wang 2016 University of Nebraska-Lincoln

Diffractive Imaging Of A Rotational Wavepacket In Nitrogen Molecules With Femtosecond Megaelectronvolt Electron Pulses, Jie Yang, Markus Guehr, Theodore Vecchione, Matthew S. Robinson, Renkai Li, Nick Hartmann, Xiaozhe Shen, Ryan Coffee, Jeff Corbett, Alan Fry, Kelly Gaffney, Tais Gorkhover, Carsten Hast, Keith Jobe, Igor Makasyuk, Alexander Reid, Joseph Robinson, Sharon Vetter, Fenglin Wang, Stephen Weathersby, Charles Yoneda, Martin Centurion, Xijie Wang

Martin Centurion Publications

This work is licensed under a Creative Commons Attribution 4.0 International License.


Manipulation Of Beams Of Ultra-Relativistic Electrons To Create Femtosecond X-Ray Pulses, Jordan T. O'Neal, Austin Schulte, Rafal Rakowski, Matthias Fuchs 2016 University of Nebraska-Lincoln

Manipulation Of Beams Of Ultra-Relativistic Electrons To Create Femtosecond X-Ray Pulses, Jordan T. O'Neal, Austin Schulte, Rafal Rakowski, Matthias Fuchs

UCARE Research Products

The research proposed here is expected to result in a crucial component used in a next-generation X-ray source. Typical conventional high-brightness X-ray sources (so-called synchrotron lightsources) are up to 30 football fields in size. Our group uses a novel technique based on ultrahigh-power lasers to develop a similar source that can readily fit into a single, university-scale laboratory. More specifically, the research conducted within this proposal will be concerned with the manipulation of beams of ultra-relativistic electrons, (electrons that move with almost the speed of light) with the goal to focus the particles into an area that is smaller than ...


Atomic Photoionization Experiment By Harmonic-Generation Spectroscopy, M. V. Frolov, T. S. Sarantseva, N. L. Manakov, K. D. Fulfer, B. P. Wilson, J. Troß, X. Ren, Erwin D. Poliakoff, A. A. Silaev, N. V. Vvedenskii, Anthony F. Starace, C. A. Trallero-Herrero 2016 Voronezh State University, Russia

Atomic Photoionization Experiment By Harmonic-Generation Spectroscopy, M. V. Frolov, T. S. Sarantseva, N. L. Manakov, K. D. Fulfer, B. P. Wilson, J. Troß, X. Ren, Erwin D. Poliakoff, A. A. Silaev, N. V. Vvedenskii, Anthony F. Starace, C. A. Trallero-Herrero

Anthony F. Starace Publications

Measurements of the high-order-harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter.


The Subject Librarian Newsletter, Creol, Spring 2016, Patti McCall 2016 University of Central Florida

The Subject Librarian Newsletter, Creol, Spring 2016, Patti Mccall

Libraries' Newsletters

No abstract provided.


Control Of Threshold Enhancements In Harmonic Generation By Atoms In A Two-Color Laser Field With Orthogonal Polarizations, M. V. Frolov, N. L. Manakov, T. S. Sarantseva, A. A. Silaev, N. V. Vvedenskii, Anthony F. Starace 2016 Voronezh State University, Russia

Control Of Threshold Enhancements In Harmonic Generation By Atoms In A Two-Color Laser Field With Orthogonal Polarizations, M. V. Frolov, N. L. Manakov, T. S. Sarantseva, A. A. Silaev, N. V. Vvedenskii, Anthony F. Starace

Anthony F. Starace Publications

Threshold phenomena (or channel-closing effects) are analyzed in high-order harmonic generation (HHG) by atoms in a two-color laser field with orthogonal linearly polarized components of a fundamental field and its second harmonic. We show that the threshold behavior of HHG rates for the case of a weak second harmonic component is sensitive to the parity of a closing multiphoton ionization channel and the spatial symmetry of the initial bound state of the target atom, while for the case of comparable intensities of both components, suppression of threshold phenomena is observed as the relative phase between the components of a two-color ...


Ultrafast Imaging Of Isolated Molecules With Electron Diffraction, Martin Centurion 2016 University of Nebraska-Lincoln

Ultrafast Imaging Of Isolated Molecules With Electron Diffraction, Martin Centurion

Martin Centurion Publications

Recent advances in ultrafast electron diffraction offer the possibility to image isolated molecules with sub-Angstrom spatial resolution in ultrafast time scales. In particular, diffraction from aligned molecules has opened the door to retrieving three-dimensional structures directly from experimental data. In this manuscript we review the progress in ultrafast gas electron diffraction and discuss remaining challenges to achieve a temporal resolution of sub-100 fs, which is needed to observe the nuclear motion in chemical reactions in the gas phase.


Controlled Generation Of Comb-Like Electron Beams In Plasma Channels For Polychromatic Inverse Thomson Gamma-Ray Sources, Serge Y. Kalmykov, X. Davoine, I Ghebregziabher, R Lehe, A F. Lifschitz, B A. Shadwick 2016 University of Nebraska-Lincoln

Controlled Generation Of Comb-Like Electron Beams In Plasma Channels For Polychromatic Inverse Thomson Gamma-Ray Sources, Serge Y. Kalmykov, X. Davoine, I Ghebregziabher, R Lehe, A F. Lifschitz, B A. Shadwick

Serge Youri Kalmykov

Propagating a relativistically intense, negatively chirped laser pulse (the bandwidth > 150 nm) in a plasma channel makes it possible to generate background-free, comb-like electron beams - sequences of synchronized bunches with a low phase-space volume and controlled energy spacing. The tail of the pulse, confined in the accelerator cavity (an electron density ‘bubble’), experiences periodic focusing, while the head, which is the most intense portion of the pulse, steadily self-guides. Oscillations of the cavity size cause periodic injection of electrons from the ambient plasma, creating an electron energy comb with the number of components, their mean energy, and energy spacing dependent ...


Customizable Electron Beams From Optically Controlled Laser Plasma Acceleration For Γ-Ray Sources Based On Inverse Thomson Scattering, Serge Y. Kalmykov, X. Davoine, Isaac Ghebregziabher, Bradley A. Shadwick 2016 CEA, DAM DIF

Customizable Electron Beams From Optically Controlled Laser Plasma Acceleration For Γ-Ray Sources Based On Inverse Thomson Scattering, Serge Y. Kalmykov, X. Davoine, Isaac Ghebregziabher, Bradley A. Shadwick

Serge Youri Kalmykov

Laser wakefield acceleration of electrons in the blowout regime can be controlled by tailoring the laser pulse phase and the plasma target. The100nm-scale bandwidth and negative frequency chirp of the optical driver compensate for the nonlinear frequency red-shift imparted by wakefield excitation.This mitigates pulse self-steepening and suppresses continuous injection. The plasma channel suppresses diffraction of the pulse leading edge, further reducing self-steepening, making injection even quieter. Besides, the channel destabilizes the pulse tail confined within the accelerator cavity (the electron density “bubble”), causing oscillations in the bubble size. The resulting periodic injection generates background-free comb-like beams – sequences of synchronized ...


Shielded Radiography With A Laser-Driven Mev-Energy X-Ray Source, Shouyuan Chen, G. Golovin, Cameron Miller, Daniel Haden, Sudeep Banerjee, Ping Zhang, Cheng Liu, Jun Zhang, Baozhen Zhao, Shaun Clarke, Sara Pozzi, Donald Umstadter 2016 University of Nebraska–Lincoln

Shielded Radiography With A Laser-Driven Mev-Energy X-Ray Source, Shouyuan Chen, G. Golovin, Cameron Miller, Daniel Haden, Sudeep Banerjee, Ping Zhang, Cheng Liu, Jun Zhang, Baozhen Zhao, Shaun Clarke, Sara Pozzi, Donald Umstadter

Donald Umstadter Publications

We report the results of experimental and numerical-simulation studies of shielded radiography using narrowband MeVenergy X-rays from a compact all-laser-driven inverse-Compton-scattering X-ray light source. This recently developed Xray light source is based on a laser-wakefield accelerator with ultra-high-field gradient (GeV/cm). We demonstrate experimentally high-quality radiographic imaging (image contrast of 0.4 and signal-to-noise ratio of 2:1) of a target composed of 8-mm thick depleted uranium shielded by 80-mm thick steel, using a 6-MeV X-ray beam with a spread of 45% (FWHM) and 107 photons in a single shot. The corresponding dose of the X-ray pulse measured in front ...


Eikonal Perturbation Theory In Photoionization, F. Cajiao Vélez, Katarzyna Krajewska, J. Z. Kamiński 2016 University of Warsaw

Eikonal Perturbation Theory In Photoionization, F. Cajiao Vélez, Katarzyna Krajewska, J. Z. Kamiński

Faculty Publications, Department of Physics and Astronomy

The eikonal perturbation theory is formulated and applied to photoionization by strong laser pulses. A special emphasis is put on the first order approximation with respect to the binding potential, which is known as the generalized eikonal approximation [2015 Phys. Rev. A 91 053417]. The ordinary eikonal approximation and its domain of applicability is derived from the generalized eikonal approximation. While the former approach is singular for the electron trajectories which return to the potential center, the generalized eikonal avoids this problem. This property makes it a promising tool for further investigations of rescattering and high-order harmonic generation processes.


Control And Optimization Of A Staged Laser-Wakefield Accelerator, Grigory V. Golovin, Sudeep Banerjee, Shouyuan Chen, N. Powers, Cheng Liu, Wenchao Yan, Jia Zhang, Ping Zhang, Baozhen Zhao, Donald Umstadter 2016 University of Nebraska-Lincoln

Control And Optimization Of A Staged Laser-Wakefield Accelerator, Grigory V. Golovin, Sudeep Banerjee, Shouyuan Chen, N. Powers, Cheng Liu, Wenchao Yan, Jia Zhang, Ping Zhang, Baozhen Zhao, Donald Umstadter

Donald Umstadter Publications

We report results of an experimental study of laser-wakefield acceleration of electrons, using a staged device based on a double-jet gas target that enables independent injection and acceleration stages. This novel scheme is shown to produce stable, quasi-monoenergetic, and tunable electron beams. We show that optimal accelerator performance is achieved by systematic variation of five critical parameters. For the injection stage, we show that the amount of trapped charge is controlled by the gas density, composition, and laser power. For the acceleration stage, the gas density and the length of the jet are found to determine the final electron energy ...


Theoretical Estimates Of Spherical And Chromatic Aberration In Photoemission Electron Microscopy, Joseph P. S. Fitzgerald, Robert Campbell Word, Rolf Kӧnenkamp 2016 Portland State University

Theoretical Estimates Of Spherical And Chromatic Aberration In Photoemission Electron Microscopy, Joseph P. S. Fitzgerald, Robert Campbell Word, Rolf Kӧnenkamp

Physics Faculty Publications and Presentations

We present theoretical estimates of the mean coefficients of spherical and chromatic aberration for low energy photoemission electron microscopy (PEEM). Using simple analytic models, we find that the aberration coefficients depend primarily on the difference between the photon energy and the photoemission threshold, as expected. However, the shape of the photoelectron spectral distribution impacts the coefficients by up to 30%. These estimates should allow more precise correction of aberration in PEEM in experimental situations where the aberration coefficients and precise electron energy distribution cannot be readily measured.


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