Recent Progress in Strong-Field Atomic and Molecular Physics

A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 6330

Special Issue Editor


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Guest Editor
Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
Interests: multiphoton and strong-field Ionization; high-harmonic generation; ultrafast optics

Special Issue Information

Dear Colleagues,

Benefiting from the invention of the chirped-pulse-amplification technique in the 1980s, which enabled the generation of near-infrared ultrashort laser pulses whose field strength commensurate with those which keep atoms and molecules together and pulse duration comparable with the time scales of electronic and molecular dynamics, a wealth of remarkable results in strong-field atomic physics emerged by the end of the 1980s and the early 1990s. In particular, the intuitive semiclassical picture of electron rescattering resulted in transformative gains in the understanding of numerous strong-field phenomena, which also inspired exciting new applications since the 2000s including the generation of attosecond pulses, absolute measurement of carrier-to-envelope phase, ultrafast molecular imaging by rescattering electrons, etc. Over the last two decades, novel laser sources and detection techniques and the influx of new ideas have continued to drive the field towards new discoveries. Moreover, investigations of strong-field processes have been extended to condensed matter systems.

Hoping to inspire new insights and innovations in the many areas related to strong-field physics, we establish this Special Issue that focuses on recent theoretical and experimental developments in strong-field physics. Topics of interest include, but are not limited to, the following areas:

  • Multiphoton and tunnel ionization
  • Dynamics of electron rescattering
  • Multielectron effects in strong-field processes
  • Molecular vibration and dissociation induced by ultrafast pulses
  • High harmonic generation in gases, solids, and plasmas
  • Attosecond pulses: generation and applications
  • Ultrafast measurement techniques
  • New developments of intense ultrafast light sources

Dr. Yu Hang Lai
Guest Editor

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Keywords

  • strong-field, multiphoton ionization
  • tunnel ionization
  • electron rescattering
  • high harmonic generation
  • attosecond pulses
  • ultrafast molecular dynamics
  • ultrafast intense lasers

Published Papers (5 papers)

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Research

12 pages, 7517 KiB  
Article
Tunability of Half Cycle Cutoff Harmonics with Inhomogeneously Enhanced Laser Pulse
by Ankur Mandal
Atoms 2023, 11(8), 113; https://doi.org/10.3390/atoms11080113 - 18 Aug 2023
Viewed by 933
Abstract
For homogeneous driving, half cycle harmonics and its corresponding half cycle cutoff (HCO) show prominent spectral features, allowing one to produce an isolated attosecond pulse with suitable filtering, or vice versa the retrieval of the driving pulse itself. The temporal profile and spatial [...] Read more.
For homogeneous driving, half cycle harmonics and its corresponding half cycle cutoff (HCO) show prominent spectral features, allowing one to produce an isolated attosecond pulse with suitable filtering, or vice versa the retrieval of the driving pulse itself. The temporal profile and spatial dependence of the inhomogeneously enhanced field are two important factors that determine the high harmonic generation (HHG) near a plasmonic nanostructure. This leads us to the question of how the HHG spectra and, in particular, the corresponding half cycle harmonics modify with different types of inhomogeneously enhanced fields. To elucidate this, we have made a comparative study of the HHG in three different types of inhomogeneously enhanced laser pulses by employing the time-dependent Schrödinger equation in one dimension. Within our chosen parameter range, the HCO in cutoff and mid-plateau regimes shift towards higher order with the increase of strength of the inhomogeneity in isotropic case. In anisotropic inhomogeneity, the cutoff HCO shifts towards the higher order but the mid-plateau HCO shifts towards lower order with the increase of strength of inhomogeneity. With increasing carrier envelope phase (CEP), the enhanced HCO in the lower-order harmonic region shifts towards higher orders. This shift is nearly linear from near the above threshold to mid-plateau region and becomes saturated in the near cutoff region. The harmonic spectra is modulo-π periodic for the isotropic inhomogeneity and it is modulo-2π periodic for the anisotropic inhomogeneity. This extension of periodicity increases the tunability of the enhanced HCO harmonics with CEP in the anisotropic inhomogeneity than the CEP tuning of the HCO harmonics in the isotropic inhomogeneity or vice versa the retrieval of CEP. Full article
(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)
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8 pages, 2626 KiB  
Article
Role of Gas Pressure in Quasi-Phase Matching in High Harmonics Driven by Two-Color Laser Field
by Sergey Stremoukhov
Atoms 2023, 11(7), 103; https://doi.org/10.3390/atoms11070103 - 7 Jul 2023
Viewed by 951
Abstract
The results of a study on the effect of pressure in a medium consisting of a set of gas jets separated by vacuum gaps, interacting with two-color laser fields formed by the fundamental and the second harmonics of a laser, are presented herein. [...] Read more.
The results of a study on the effect of pressure in a medium consisting of a set of gas jets separated by vacuum gaps, interacting with two-color laser fields formed by the fundamental and the second harmonics of a laser, are presented herein. It has been demonstrated that a decrease in pressure leads to a shift in the region of harmonics where quasi-phase matching (QPM) occurs towards shorter wavelength radiation, accompanied by an increase in the efficiency of amplification of these harmonics. A feature of this process is the identical power-law character of the shift in the region and the increase in the efficiency of harmonic QPM amplification. Additionally, the study presents the results of the effect of inaccurately setting the width of the gas jets on the shape of the spectrum of harmonic QPM amplification. Full article
(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)
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11 pages, 3248 KiB  
Article
Pulse Cycle Dependent Nondipole Effects in Above-Threshold Ionization
by Danish Furekh Dar and Stephan Fritzsche
Atoms 2023, 11(6), 97; https://doi.org/10.3390/atoms11060097 - 12 Jun 2023
Viewed by 1183
Abstract
In this study, we employ strong field approximation (SFA) to investigate the influence of the number of pulse cycles on above-threshold ionization within the framework of nondipole theory. The SFA enables the analysis of the ionization process under the dominance of the electric [...] Read more.
In this study, we employ strong field approximation (SFA) to investigate the influence of the number of pulse cycles on above-threshold ionization within the framework of nondipole theory. The SFA enables the analysis of the ionization process under the dominance of the electric field, compared to other factors such as the binding potential of an atom. Nondipole effects, including higher-order multipole fields, can significantly impact ionization dynamics. However, the interaction between nondipole effects and pulse cycles remains unclear. Therefore, we investigate the pulse cycle dependence of ionization and examine peak shifts in Kr and Ar atoms. Our findings have implications for comprehensively understanding the effects of electromagnetic fields on electron behavior. The insights gained from this study provide valuable guidance for future research in strong field ionization. Full article
(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)
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24 pages, 6178 KiB  
Article
Modification of Vibrational Parameters of a CO2 Molecule by a Laser Field: Impact on Tunnel Ionization
by Aleksei S. Kornev and Vladislav E. Chernov
Atoms 2023, 11(6), 92; https://doi.org/10.3390/atoms11060092 - 5 Jun 2023
Viewed by 1166
Abstract
In this paper, we theoretically study the laser-induced modification of the vibrational parameters of a carbon dioxide molecule regarding its tunnel ionization. Our study predicts a 5% increase in the ionization rate in anti-Stokes channels that corresponds to pumping the Σu mode [...] Read more.
In this paper, we theoretically study the laser-induced modification of the vibrational parameters of a carbon dioxide molecule regarding its tunnel ionization. Our study predicts a 5% increase in the ionization rate in anti-Stokes channels that corresponds to pumping the Σu mode up to vai=10. The molecule is imparted with an additional energy from the pre-pumped vibrational states, which is absorbed during ionization. As a result, the tunneling rate increases. This amplification of tunnel ionization of the CO2 gas target can potentially be used for the laser separation of carbon isotopes. Full article
(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)
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12 pages, 1042 KiB  
Article
High-Order Above-Threshold Ionization Using a Bi-Elliptic Orthogonal Two-Color Laser Field with Optimal Field Parameters
by Abdulah S. Jašarević, Elvedin Hasović and Dejan B. Milošević
Atoms 2023, 11(6), 91; https://doi.org/10.3390/atoms11060091 - 5 Jun 2023
Viewed by 1140
Abstract
In the present paper, we study the high-order above-threshold ionization of noble-gas atoms using a bi-elliptic orthogonal two-color (BEOTC) field. We give an overview of the SFA theory and calculate the differential ionization rate for various values of the laser field parameters. We [...] Read more.
In the present paper, we study the high-order above-threshold ionization of noble-gas atoms using a bi-elliptic orthogonal two-color (BEOTC) field. We give an overview of the SFA theory and calculate the differential ionization rate for various values of the laser field parameters. We show that the ionization rate strongly depends on the ellipticity and the relative phase between two field components. Using numerical optimization, we find the values of ellipticity and relative phase that maximize the ionization rate at energies close to the cutoff energy. To explain the obtained results, we present, to the best of our knowledge, for the first time the quantum-orbit analysis in the BEOTC field. We find and classify the saddle-point (SP) solutions and study their contributions to the total ionization rate. We analyze quantum orbits and corresponding velocities to explain the contribution of relevant SP solutions. Full article
(This article belongs to the Special Issue Recent Progress in Strong-Field Atomic and Molecular Physics)
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