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Results for “electron rescattering”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Quasi-classical model of electron rescattering in fields of intense infrared and weak high-frequency laser pulses

We study the influence of a weak high-frequency [in the extreme ultraviolet (XUV) region] laser pulse on the mechanism of electron rescattering on the parent ion in the processes of high harmonic generation and above-threshold ionisation induced by an intense infrared (IR) laser field. Two scenarios of the three-step rescattering are discussed: with the absorption of the XUV photon at the ionisation step of an atom and with the absorption/emission of a XUV photon at the moment of recombination or scattering of the electron returned by the IR field to the parent ion. Estimates are obtained for the high-energy plateau cutoff positions in the spectra of harmonic generation and above-threshold ionisation. (paper)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Influence of orbital symmetry on diffraction imaging with rescattering electron wave packets

The ability to directly follow and time-resolve the rearrangement of the nuclei within molecules is a frontier of science that requires atomic spatial and few-femtosecond temporal resolutions. While laser-induced electron diffraction can meet these requirements, it was recently concluded that molecules with particular orbital symmetries (such as pg) cannot be imaged using purely backscattering electron wave packets without molecular alignment. Here, we demonstrate, in direct contradiction to these findings, that the orientation and shape of molecular orbitals presents no impediment for retrieving molecular structure with adequate sampling of the momentum transfer space. We overcome previous issues by showcasing retrieval of the structure of randomly oriented O 2 and C 2 H 2 molecules, with π g and π u symmetries, respectively, and where their ionization probabilities do not maximize along their molecular axes. As a result, while this removes a serious bottleneck for laser-induced diffraction imaging, we find unexpectedly strong backscattering contributions from low-Z atoms.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

New Directions in Strong-Field Control

The thrust of our AMOS-supported research was initially the problem of strong-field alignment in complex systems. Over the years, this research was generalized to strong field coherent control, including alignment, three-dimensional alignment, torsional control and molecular focusing in moderately intense laser fields. A second, related theme that was added to our AMOS-supported research was the physics, theory and potential applications of high harmonic generation from aligned molecules. This second thrust was motivated by the intense interest of the AMOS Program in attosecond science and rescattering electrons physics, and has been carried out in collaboration with AMOS experimentalists colleagues. This research led to 60 peer refereed publications.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Controlling electron-ion rescattering in two-color circularly polarized femtosecond laser fields

High-harmonic generation driven by two-color counter-rotating circularly polarized laser fields was recently demonstrated experimentally as a breakthrough source of bright, coherent, circularly polarized beams in the extreme ultraviolet and soft-x-ray regions. However, the conditions for optimizing the single-atom yield are significantly more complex than for linearly polarized driving lasers and are not fully understood. In this study we present a comprehensive study of strong-field ionization—the complementary process to high-harmonic generation—driven by two-color circularly polarized fields. We uncover the conditions that lead to enhanced electron-ion rescattering, which should correspond to the highest single-atom harmonic flux. Using a velocity map imaging photoelectron spectrometer and tomographic reconstruction techniques, we record three-dimensional photoelectron distributions resulting from the strong-field ionization of argon atoms across a broad range of driving laser intensity ratios. In combination with analytical predictions and advanced numerical simulations, we show that “hard” electron-ion rescattering is optimized when the second-harmonic field has an intensity approximately four times higher than that of the fundamental driving field. We also investigate electron-ion rescattering with co-rotating fields, and find that rescattering is significantly suppressed when compared with counter-rotating fields.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Enhanced Strong-Field Ionization and Fragmentation of Methanol Using Noncommensurate Fields

Electron-initiated chemistry with chemically relevant electron energies (10–200 eV) is at the heart of several high-energy processes and phenomena. To probe these dissociation and fragmentation reactions with femtosecond resolution requires the use of femtosecond lasers to induce ionization of the polyatomic molecules via electron rescattering. Here, we combine noncommensurate fields with intensity-difference spectra using methanol as a model system. Experimentally, we find orders of magnitude enhancement in several product ions of methanol when comparing coherent vs incoherent combinations of noncommensurate fields. This approach not only mitigates multiphoton ionization and multicycle effects during ionization but also enhances tunnel ionization and electron rescattering energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

High-energy electron emission from metallic nano-tips driven by intense single-cycle terahertz pulses

Electrons ejected from atoms and subsequently driven to high energies in strong laser fields enable techniques from attosecond pulse generation to imaging with rescattered electrons. Analogous processes govern strong-field electron emission from nanostructures, where long wavelength radiation and large local field enhancements hold the promise for producing electrons with substantially higher energies, allowing for higher resolution time-resolved imaging. Here we report on the use of single-cycle terahertz pulses to drive electron emission from unbiased nano-tips. Energies exceeding 5 keV are observed, substantially greater than previously attained at higher drive frequencies. Despite large differences in the magnitude of the respective local fields, we find that the maximum electron energies are only weakly dependent on the tip radius, for 10 nm<R<1,000 nm. As a result, due to the single-cycle nature of the field, the high-energy electron emission is predicted to be confined to a single burst, potentially enabling a variety of applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Femtosecond intramolecular rearrangement of the CH 3 NCS radical cation

Strong-field ionization, involving tunnel ionization and electron rescattering, enables femtosecond time-resolved dynamics measurements of chemical reactions involving radical cations. Here, we compare the formation of CH 3 S + following the strong-field ionization of the isomers CH 3 SCN and CH 3 NCS. The former involves the release of neutral CN, while the latter involves an intramolecular rearrangement. Here, we find the intramolecular rearrangement takes place on a single picosecond timescale and exhibits vibrational coherence. Density functional theory and coupled-cluster calculations on the neutral and singly ionized species help us determine the driving force responsible for intramolecular rearrangement in CH 3 NCS. Our findings illustrate the complexity that accompanies radical cation chemistry following electron ionization and demonstrate a useful tool for understanding cation dynamics after ionization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Searching for optimal THz generation through calculations of the asymmetry of photoelectron momentum distributions by an improved strong-field-approximation method

From the solution of the time-dependent Schrödinger equation (TDSE), it has been shown that in a two-color laser pulse the relative phase that optimizes terahertz (THz) radiation also optimizes the asymmetry of the angular distribution of photoelectrons. Here, in this work, we show that a second-order strong-field approximation can accurately calculate the asymmetry of photoelectrons and thus can locate the phase delay that optimizes THz generation, doing so four orders of magnitude faster than TDSE calculations. We further trace that this is possible because THz emission originates from a free-free radiative transition between the rescattered electron and the target ion, similar to other electron-ion collisions in the laser field, e.g., high-harmonic generation and nonsequential double ionization. Our results pave the way to locate the optimal phase delay for any typical laser pulses for maximal THz generation in the laboratory.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Wavelength and intensity dependence of recollision-enhanced multielectron effects in high-order harmonic generation

Using a model molecular system (A 2 ) with two active electrons restricted to one dimension, we examine high-order harmonic generation (HHG) enhanced by rescattering. Our results show that even at intensities well below the single ionization saturation, harmonics generated from the cation (A 2 + ) can be significantly enhanced due to the rescattering of the electron that is initially ionized. This two-electron effect is manifested by the appearance of a secondary plateau and cutoff in the HHG spectrum, extending beyond the predicted cutoff in the single active electron approximation. We use our molecular model to investigate the wavelength dependence of rescattering enhanced HHG, which was first reported in a model atomic system [I. Tikhomirov, T. Sato, and K. L. Ishikawa, Phys. Rev. Lett. 118, 203202 (2017)]. Finally, we demonstrate that the HHG yield in the secondary cutoff is highly sensitive to the available electron rescattering energies as indicated by a dramatic scaling with respect to driving wavelength.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Interference stabilization of atoms in a strong laser field for obtaining inversion and lasing in the visible and VUV frequency ranges

The interference stabilization of Rydberg atoms in strong laser fields is proposed for producing a plasma channel with the inverse population. Inversion between a group of Rydberg levels and low-lying excited levels and the ground state permits amplification and lasing in the IR, visible, and VUV frequency ranges. The lasing and light amplification processes in the plasma channel are analyzed using rate equations and the efficiency of this method is compared with that in the usual method for high harmonic generation during rescattering of electrons by a parent ion.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Controlling Nonsequential Double Ionization in Two-Color Circularly Polarized Femtosecond Laser Fields

Atoms undergoing strong-field ionization in two-color circularly polarized femtosecond laser fields exhibit unique two-dimensional photoelectron trajectories and can emit bright circularly polarized extreme ultraviolet and soft-x-ray beams. Here, we present the first experimental observation of nonsequential double ionization in these tailored laser fields. Moreover, we can enhance or suppress nonsequential double ionization by changing the intensity ratio and helicity of the two driving laser fields to maximize or minimize high-energy electron-ion rescattering. Our experimental results are explained through classical simulations, which also provide insight into how to optimize the generation of circularly polarized high harmonic beams.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Atomic and Molecular Physics in Strong Fields

In this project, we have investigated a broad range of atomic, molecular, and optical (AMO) processes of current significance in strong-field and ultrafast science and technology. The main goals are to develop new theoretical formalisms and accurate computational methods for ab initio and in-depth non-perturbative study of time-resolved multiphoton quantum dynamics and spectroscopy, very-high-order harmonic generation, optimal control of ultrafast attosecond pulse generation, and resonance-enhanced below threshold harmonics in intense ultrashort laser fields. We have worked on the following projects and we have published 20 top 15 % SCI journal articles during the last 3.5 years (Jan. 1, 2016 to June 30, 2019), including one article in top raking Physical Review Letters, and 3 articles in top ranking (Nature) Scientific Reports, and one Physical Review A article was chosen as Editors’ suggestion paper, etc. (a) Development of new time-dependent methods for accurate and efficient solution of multi-dimensional time-dependent Schrödinger equation and time-dependent density functional theory. (b) Non-perturbative treatment of very-high order (1000th – 5000th order) harmonic generation and broadband supercontinuum spectra from XUV to soft x-ray regime. (c) Development of synchrosqueezing transform (SST) for precision time-frequency analysis of electron multi-rescattering dynamics. (d) Exploration of the dynamical origin of resonance-enhanced near- and below-threshold harmonics. (e) Probing the high-order harmonics generation in disordered semiconductor. (f) Multiphoton ionization of one-electron relativistic diatomic quasi-molecules in strong laser fields. and, (g) New development of non-adiabatic density functional theory. The theoretical and simulation projects we have pursued are closely related to the ongoing experimental researches in several leading laboratories in the US and Europe, etc. It is expected that the outcome of this project will provide timely and significant new information and insight for the advancement of strong-field atomic and molecular physics and ultrafast science and technology.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Proton transparency and neutrino physics: New methods and modeling

Extracting accurate results from neutrino oscillation and cross section experiments requires accurate simulation of the neutrino-nucleus interaction. The rescattering of outgoing hadrons (final state interactions) by the rest of the nucleus is an important component of these interactions. We present a new measurement of proton transparency (defined as the fraction of outgoing protons that emerge without significant rescattering) using electron-nucleus scattering data recorded by the CLAS detector at Jefferson Laboratory on helium, carbon, and iron targets. This analysis uses a new data-driven method to extract the transparency. It defines transparency as the ratio of electron-scattering events with a detected proton to quasi-elastic electron-scattering events where a proton should have been knocked out. Our results are consistent with previous measurements that determined the transparency from the ratio of measured events to theoretically predicted events. We find that the GENIE event generator, which is widely used by oscillation experiments to simulate neutrino-nucleus interactions, needs to better describe both the nuclear ground state and proton rescattering in order to reproduce our measured transparency ratios, especially at lower proton momenta.

direct reactions↗
DOE OSTI2023

Enhanced cutoff energies for direct and rescattered strong-field photoelectron emission of plasmonic nanoparticles

Abstract The efficient generation, accurate detection, and detailed physical tracking of energetic electrons are of applied interest for high harmonics generation, electron-impact spectroscopy, and femtosecond time-resolved scanning tunneling microscopy. We here investigate the generation of photoelectrons (PEs) by exposing plasmonic nanostructures to intense laser pulses in the infrared (IR) spectral regime and analyze the sensitivity of PE spectra to competing elementary interactions for direct and rescattered photoemission pathways. Specifically, we measured and numerically simulated emitted PE momentum distributions from prototypical spherical gold nanoparticles (NPs) with diameters between 5 and 70 nm generated by short laser pulses with peak intensities of 8.0 × 10 12 and 1.2 × 10 13 W/cm 2 , demonstrating the shaping of PE spectra by the Coulomb repulsion between PEs, accumulating residual charges on the NP, and induced plasmonic electric fields. Compared to well-understood rescattering PE cutoff energies for strong-field photoemission from gaseous atomic targets (10× the ponderomotive energy), our measured and simulated PE spectra reveal a dramatic cutoff-energy increase of two orders of magnitude with a significantly higher contribution from direct photoemission. Our findings indicate that direct PEs reach up to 93 % of the rescattered electron cutoff energy, in contrast to 20 % for gaseous atoms, suggesting a novel scheme for the development of compact tunable tabletop electron sources.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Photoelectron holographic interferences from multiple returning in strong-field tunneling ionization

By numerically solving the time-dependent Schrödinger equation, we theoretically investigate the holographic structure of the multiple-returning rescattering recorded in the photoelectron momentum distribution. In the orthogonally polarized two-color fields, we show that the interference patterns periodically oscillate with the relative phase. Tracing the relative phase where the oscillation minimizes, we find that the dependences of the phase on the parallel momentum for the first-returning and the second-returning rescattering holographic interferences are different. With the quantum-orbit model, we demonstrated that the difference is related to the ionization and rescattering times of the electron. Moreover, we show that the influence of the Coulomb interaction on the oscillation of both the first-returning rescattering and the second-returning rescattering holographic interferences can be ignored. This suggests us that the temporal characteristics of the electron can be resolved by analyzing the relative phase’s dependence of the multiple-returning holographic interference.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Origin of the multiphoton-regime harmonic-generation plateau structure

A physical interpretation is provided for the formation of the multiphoton-regime plateau feature in the spectra of nonlinear and correlated process of high-order harmonic generation (HHG) of two-active-electron atoms interacting with an intense linearly polarized laser field. While in the strong-field tunneling regime the plateau feature is well known to be due to rescattering effects of the freed electron, its counterpart in the multiphoton regime is due to atomic resonance effects involving both singly excited states and doubly excited states. Here, we propose a strategy to uncover which kind of these states are responsible for this phenomenon. By studying the sensitivity of HHG to the initial state in helium, in this work we show that this multiphoton-regime plateau structure mostly originates from singly excited states.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Exploration of laser-driven electron-multirescattering dynamics in high-order harmonic generation

Multiple rescattering processes play an important role in high-order harmonic generation (HHG) in an intense laser field. However, the underlying multi-rescattering dynamics are still largely unexplored. Here we investigate the dynamical origin of multiple rescattering processes in HHG associated with the odd and even number of returning times of the electron to the parent ion. We perform fully ab initio quantum calculations and extend the empirical mode decomposition method to extract the individual multiple scattering contributions in HHG. We find that the tunneling ionization regime is responsible for the odd number times of rescattering and the corresponding short trajectories are dominant. On the other hand, the multiphoton ionization regime is responsible for the even number times of rescattering and the corresponding long trajectories are dominant. Moreover, we discover that the multiphoton- and tunneling-ionization regimes in multiple rescattering processes occur alternatively. Our results uncover the dynamical origin of multiple rescattering processes in HHG for the first time. As a result, it also provides new insight regarding the control of the multiple rescattering processes for the optimal generation of ultrabroad band supercontinuum spectra and the production of single ultrashort attosecond laser pulse.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Extraction of geometrical structure of ethylene molecules by laser-induced electron diffraction combined with ab initio scattering calculations

In this paper, we measured angle-resolved high-energy electron spectra emitted from ${\mathrm{C}}_{2}{\mathrm{H}}_{4}$ in an intense laser field, extracted field-free electron-ion elastic scattering differential cross sections (DCSs) according to quantitative rescattering theory, and obtained molecular contrast factors (MCFs) subtracting the incoherent sum of DCSs of all the atoms in the molecule. Comparing the results with ab initio scattering calculations and employing least-squares fitting, we have extracted the C-C and C-H bond lengths of the molecule with ${\sim}5$ % uncertainty. Finally, this approach opens the way to retrieve the structure of hydrocarbon molecules, potentially at high temporal resolution, employing low collision energies where electron scattering is sensitive to the hydrogen atoms; and where the independent atom model calculations may fail to reproduce the experimentally extracted MCF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗