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Results for “ELECTROMAGNETIC PULSES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Excitation of Nonlinear Spin Oscillations in an Antiferromagnet under the Action of Pulsed Terahertz Pumping

We present a model of excitation of nonlinear spin oscillations in an antiferromagnet under the action of terahertz pulses of an electromagnetic field. It is shown that, with increasing pumping pulse amplitude, the spin system response increases linearly in the fundamental (resonant) quasi-ferromagnetic mode and quadratically in the second harmonic. We have compared the theoretically obtained dependences of the intensities of the sample response amplitudes for the fundamental mode and the second harmonic with the experimental ones. The comparison demonstrates the applicability of the developed method of analyzing dynamic processes in antiferromagnets occurring under the action of terahertz electromagnetic pulses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Normal modes of strictly resonant and quasi-resonant regimes of electromagnetically induced transparency

We report the results of a theoretical study of the evolution of a probe pulse under electromagnetically induced transparency conditions in the lambda scheme of degenerate inhomogeneously broadened quantum transitions. It is assumed that the interacting fields are elliptically polarised, and their effect on the medium can be either strictly resonant or quasi-resonant. It is shown that probe light in a medium can be represented as the sum of two normal modes, i.e. quasi-monochromatic elliptically polarised fields propagating independently of each other. The major axis of the polarisation ellipse of the normal mode of the first type is parallel, and that of the second type is perpendicular to the major axis of the polarisation ellipse of the control light. Due to the fact that velocities of normal-mode pulses are different, a single probe pulse entering a medium splits into individual pulses inside the medium, each of which transfers the energy of one of the normal modes. In the case of quasi-resonance, the splitting occurs at a shorter distance than in the case of strict resonance. If normal modes are not phase modulated at the input surface of the medium, then in the case of quasi-resonance they become phase modulated during their propagation inside the medium, whereas this does not occur in the case of strict resonance. It is shown that in the case of quasi-resonance, the phase modulation value of the mode of the second of the above types significantly exceeds that of the first type. The medium transparency for the normal mode of the first type slightly decreases with the transition from the case of strict resonance to the case of quasi-resonance, while the medium transparency for the mode of the second type decreases significantly. The total probe field, which is the sum of the normal modes, has phase modulation before it splits into mode pulses in cases of both strict resonance and quasi-resonance, even if it does not have it on the input surface. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Manipulating and Probing Ultrafast Atomic and Molecular Dynamics (Final Report)

This program has focused on the exploration and control of dynamics in atoms, small molecules, clusters, and micro- or nano-structures following ultrafast excitation and/or driven by strong oscillating fields. In our principal experiments, gas phase atoms and molecules were exposed to short pulses of electromagnetic radiation with frequencies ranging from THz into the XUV spectral regions, and with durations from picoseconds to attoseconds. The pulses coherently induce and/or probe dynamics in the electronic, vibrational, and rotational degrees of freedom of the targets. The overarching goal of the various projects has been to exploit strong-field processes and/or implement novel ultrafast techniques for manipulating and probing coherent electronic and nuclear motion. Typically, the relevant system evolution occurs over attosecond to picosecond timescales. In doing so, we have gained a more complete picture of correlated multi-particle dynamics in atoms, molecules, and other complex systems and expanded the toolbox of useful techniques for manipulating and probing those dynamics. Grant funds were primarily used to: (i) pay salaries and fringe benefits for the PI and postdocs and stipends, tuition, and health care costs for graduate students; (ii) cover travel expenses for the PI, postdocs, and students to attend and participate in professional meetings, conferences, and workshops; and (iii) purchase research materials, supplies, and equipment required for experiments. The research resulted in the publication of 24 peer reviewed articles (including 1 in Nature Physics, 2 in Nature Communications, 7 in Physical Review Letters, and 12 in Physical Review A), and 4 PhD dissertations. The specific results from different funding periods are summarized separately in the main report.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Pulse joining cartridges

A pulsed joining tool includes a tool body that defines a cavity that receives an inner tubular member and an outer tubular member and a pulse joining cartridge. The tubular members are nested together with the cartridge being disposed around the outer tubular member. The cartridge includes a conductor, such as a wire or foil, that extends around the outer tubular member and is insulated to separate a supply segment from a return segment. A source of stored electrical energy is discharged through the conductor to join the tubular members with an electromagnetic force pulse.

25 ENERGY STORAGE↗
DOE OSTI2019

Methodology for Volume Reduction of Radioactive Metallic Waste - 19491

A decontamination methodology for out-of-core nuclear reactor alloys is being developed to reduce the volume of low- and intermediate-level radioactive metallic wastes. For out-of-core reactor metals contamination is limited to surface oxides. For surface oxide removal a technology based on laser ablation is being explored. This paper presents work performed to identify the key parameters that affect the efficiency of removal of surface oxides from out-of-core reactor metals and alloys. This study examined carbon steel (used for coolant feeder pipes of CANDU{sup R} reactors) as a model reactor material. The morphology and thickness of oxides on a used feeder pipe vary considerably depending on its service life and the location along the pipe. Hence, oxides with different morphologies and thicknesses were first grown by corroding carbon steel coupons under different solution conditions. The oxides formed ranged from thin layers of uniformly distributed mixed Fe{sup II}/Fe{sup III} hydroxides/oxides to dual layers consisting of ferric oxide/oxyhydroxide islands with thickness up to 200 μm on top of the more uniformly distributed mixed Fe{sup II}/Fe{sup III} layer. Removal of these oxides was performed using a 1064 nm pulsed laser. Of the laser parameters tested, the pulse radiance was found to be the most important. Four radiances ranging from 5 to 200 MW/cm{sup 2} were used. At radiances higher than 100 MW/cm{sup 2}, single pulses were sufficient to remove both types of oxides, but also extensively melted the metal substrate. At lower radiances, multiple pulses were required to remove the oxides completely, but caused less damage to the metal substrate. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Low-coherence interferometry as a tool for monitoring laser micro- and nanoprocessing of diamond surfaces

We have demonstrated the possibility of using low-coherence tandem optical interferometry for monitoring the local laser processing of diamond surfaces. Noncontact measurements of the optical thickness of single-crystal diamond plates were performed directly during the exposure of the surface to repetitive intense laser pulses. We investigated the dynamics of the thinning of a single crystal in two radically different regimes of laser etching: ablation (KrF excimer laser, λ = 248 nm, τ = 20 ns) and nanoablation (Ti : sapphire laser, λ = 266 nm, τ = 100 fs). (laser technologies)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Suppression of power losses during laser pulse propagation in underdense plasma slab

For current state-of-the-art terawatt lasers, the primary laser scattering mechanisms in plasma include Forward Raman Scattering (FRS), excitation of plasma waves, and the self-modulational instability (SMI). Using 2D PIC simulations, we demonstrate the dominance of the FRS in the regime with medium-to-low density plasma and non-relativistic laser fields. However, the use of multi-colored lasers with frequency detuning exceeding the plasma frequency, Δω > ω pe , suppresses the FRS. Finally, the laser power can then be transmitted efficiently.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Human umbilical cord mesenchymal stem cells regulate CD54 and CD105 in vascular endothelial cells and suppress inflammation in Kawasaki disease

Highlights: • CD31{sup +}CD54{sup +} and CD31{sup +}CD105{sup +} EMPs change inconsistently at different stages of KD, potentially reflect endothelial function. • HucMSCs suppress inflammation and regulate the expression levels of CD54 and CD105 in vascular endothelial cells in KD. • HucMSCs inhibit coronary artery inflammation while also promoting the repair of damaged tissues in KD mice. The objective was to evaluate the expression levels of CD31{sup +}CD54{sup +} and CD31{sup +}CD105{sup +} endothelial microparticles (EMPs) before and after intravenous immunoglobulin (IVIG) treatment of Kawasaki disease (KD). To explore the role of human umbilical cord mesenchymal stem cells (hucMSCs) in inhibiting endothelial inflammation in KD, the effects of hucMSCs on the expression of CD54 and CD105 in endothelial cells in KD were analyzed in vivo and in vitro.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Enhanced spatial resolution of Eljen-204 plastic scintillators for use in rep-rated proton diagnostics

A pixelated scintillator has been designed, fabricated, and tested using a laser-accelerated proton source for use in proton diagnostics at rep-rated laser facilities. The work presented here demonstrates the enhanced spatial resolution of thin, organic scintillators through a novel pixelation technique. Furthermore, experimental measurements using laser-generated protons incident onto 130 μm-thick scintillators indicate a >20% reduction in the scintillator point spread function (PSF) for the detectors tested. The best performing pixelated detector reduced the ~200 μm PSF of the stock material to ~150 μm. The fabrication technique may be tailored to reduce the pixel size and achieve higher spatial resolutions.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

CsI(Tl) pulse shape discrimination with the Belle II electromagnetic calorimeter as a novel method to improve particle identification at electron–positron colliders

Here we describe the implementation and performance of CsI(Tl) pulse shape discrimination for the Belle II electromagnetic calorimeter, representing the first application of CsI(Tl) pulse shape discrimination for particle identification at an electron–positron collider. The pulse shape characterization algorithms applied by the Belle II calorimeter are described. Control samples of $γ, μ^+, π^±, K^±$ and $ρ/ \bar{ρ}$ are used to demonstrate the significant insight into the secondary particle composition of calorimeter clusters that is provided by CsI(Tl) pulse shape discrimination. Comparisons with simulation are presented and provide further validation for newly developed CsI(Tl) scintillation response simulation techniques, which when incorporated with GEANT4 simulations allow the particle dependent scintillation response of CsI(Tl) to be modelled. Comparisons between data and simulation also demonstrate that pulse shape discrimination can be a new tool to identify sources of improvement in the simulation of hadronic interactions in materials. The $K^0_L$ efficiency and photon-as-hadron fake-rate of a multivariate classifier that is trained to use pulse shape discrimination is presented and comparisons are made to a shower-shape based approach. CsI(Tl) pulse shape discrimination is shown to reduce the photon-as-hadron fake-rate by over a factor of 3 at photon energies of 0.2 GeV and over a factor 10 at photon energies of 1 GeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Terahertz Solitons in Condensed Media

Theoretical approaches to the formation and propagation of soliton-like broadband electromagnetic and acoustic pulses with terahertz frequencies in condensed media are reviewed. Solitons of different types are analyzed and controlling their parameters by modifying the nonlinear medium is discussed. Nonlinear molecular excitations in biopolymers whose frequencies fall into the terahertz range are considered, and their interactions with external fields of resonant frequencies are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Effect of polarization on the structure of electromagnetic field and spatiotemporal distribution of e{sup +}e{sup –} pairs generated by colliding laser pulses

We have studied the production of electron–positron pairs due to polarization of vacuum in the presence of the strong electromagnetic field of two counterpropagating laser pulses. The structure of the electromagnetic field with the circular polarization has been determined using the 3D model of focused laser pulses, which was proposed by Narozhny and Fofanov. Analytic calculations have shown that the electric and magnetic fields are almost parallel to each other in the focal region when the laser pulses are completely transverse in the electric (E-wave) or magnetic (H-wave) field. On the other hand, the electric and magnetic fields are almost orthogonal when laser pulses consist of a mixture of E- and H-waves of the same amplitude. It has been found that although the latter configuration of colliding laser pulses has a much higher pair production threshold, it can generate much shorter electron–positron pulses as compared to the former configuration. The dependence of the production efficiency of pairs and their spatiotemporal distribution on the polarization of laser pulses has been analyzed using the structure of the electromagnetic field in the focal plane.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗