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Photonics
Special Issues
Atomic and Molecular Processes in Strong Laser Fields
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Atomic and Molecular Processes in Strong Laser Fields

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (10 October 2023) | Viewed by 15027

Special Issue Editor

Dr. Mikhail Yu. Ryabikin

E-Mail Website
Guest Editor
Institute of Applied Physics, Russian Academy of Sciences, 46 Ulyanov Str., 603950 Nizhny Novgorod, Russia
Interests: atomic and molecular processes in strong laser fields; attosecond physics; spectroscopy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Thanks to advances in high-power femtosecond lasers, several decades ago, it became possible to study the processes of laser–matter interaction at field strengths approaching the binding force experienced by an electron inside atoms or molecules. An adequate theoretical description of such processes requires the use of nonperturbative approaches. It is the development of such approaches that has become a key factor in understanding and satisfactorily describing a number of intriguing phenomena, such as above-threshold ionization, non-sequential ionization, and high-order harmonic generation. At the same time, early theories inevitably used a number of approximations that left out of consideration many interesting aspects of strong-field physics. In recent years, many experimental results have been obtained that expand our understanding of processes in strong fields and illuminate hitherto unknown aspects of them; in addition, there have been a number of theoretical advances that improve our ability to describe these new effects by overcoming the limitations of previous theories. In addition to their fundamental scientific significance, these advances have contributed to the expansion of experimental tools, including those for probing and controlling ultrafast processes in matter on timescales down to attoseconds.

This Special Issue aims to present the latest advances in the study of strong-field laser–matter interactions, including, among others, such topics as:

  • Coulomb effects;
  • Resonance effects;
  • Multielectron effects;
  • Nondipole effects;
  • Time delays in ionization;
  • Chirality sensitive strong-field laser–matter interactions;
  • Ultrafast nonlinear spectroscopy;
  • High harmonic spectroscopy;
  • Quantum optical aspects of strong-field processes.

Dr. Mikhail Yu. Ryabikin
Guest Editor

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Keywords

  • ionization
  • resonance effects
  • multielectron systems
  • nondipole effects
  • ionization time delays
  • circular dichroism
  • ultrafast nonlinear spectroscopy
  • HHG spectroscopy
  • quantum optics

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Published Papers (9 papers)

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Research

25 pages, 4575 KiB  
Article
Maximizing the Response of a Helium Atom at the Third Harmonic of an Intense Femtosecond Ultraviolet Pulse
by Ilias R. Khairulin, Mikhail Yu. Emelin, Maria M. Popova, Elena V. Gryzlova, Mikhail Yu. Ryabikin and Vladimir A. Antonov
Photonics 2023, 10(12), 1387; https://doi.org/10.3390/photonics10121387 - 18 Dec 2023
Viewed by 1603
Abstract
The optimal regime of three-photon resonant excitation of a helium atom via a femtosecond ultraviolet (UV) pulse was discovered and numerically studied, at which the maximum power of the third harmonic of the UV field is achieved in the spectrum of dipole acceleration [...] Read more.
The optimal regime of three-photon resonant excitation of a helium atom via a femtosecond ultraviolet (UV) pulse was discovered and numerically studied, at which the maximum power of the third harmonic of the UV field is achieved in the spectrum of dipole acceleration (the second time derivative of the induced dipole moment) of the atom. It is shown that the optimal frequency of the UV field nearly coincides with the frequency of the three-photon transition |1s2⟩–|1s2p⟩, taking into account its shift as a result of the dynamic Stark effect, and the intensity of the UV field is dictated by the condition of maximizing the product of the populations of the |1s2⟩ and |1s2p⟩ states, averaged over the time interval during which the UV field is non-zero. For the considered UV field durations, from 10 to 100 cycles of the carrier frequency (from units to tens of femtoseconds), the optimal intensity lies in the range from 1014 W/cm2 to several units of 1014 W/cm2. It is shown that with an optimal choice of the frequency and intensity of the UV field, the dynamics of excitation of bound and continuum states, as well as the shape of the time envelope of the dipole acceleration of the atom, weakly depend on the duration of the UV field envelope; only their time scale changes significantly. In addition, under optimal conditions, the average power of the third harmonic signal in the dipole acceleration spectrum is practically independent of the duration of the UV field envelope. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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13 pages, 5267 KiB  
Article
Determining the Orbital Angular Momentum of a Vortex Beam Using Strong Field Ionization
by Harrison Pasquinilli, Alex Schimmoller, Spencer Walker and Alexandra S. Landsman
Photonics 2023, 10(12), 1322; https://doi.org/10.3390/photonics10121322 - 29 Nov 2023
Cited by 2 | Viewed by 1727
Abstract
While interferometric methods exist for classifying vortex states of light, these techniques usually require destroying the beam of interest to determine the light’s OAM. A recent two-color pump-probe experiment employed strong field ionization and beam sculpting to classify vortex beams. Here, we propose [...] Read more.
While interferometric methods exist for classifying vortex states of light, these techniques usually require destroying the beam of interest to determine the light’s OAM. A recent two-color pump-probe experiment employed strong field ionization and beam sculpting to classify vortex beams. Here, we propose an alternative strong-field method for distinguishing OAM states of light which does not require beam sculpting and instead utilizes a noncollinear terahertz standing wave to probe ionized electrons. We then use classical trajectory Monte Carlo (CTMC) methods to simulate strong-field ionization of helium under this configuration with the terahertz field both on and off. We find that the resulting electron momenta distributions can be used to extract the OAM of the beam, as long as the vortex beam spot size does not exceed 1/4 the terahertz pulse’s wavelength. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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11 pages, 642 KiB  
Article
Acceleration of Neutral Atoms by Strong Short-Wavelength Short-Range Electromagnetic Pulses
by Vladimir S. Melezhik and Sara Shadmehri
Photonics 2023, 10(12), 1290; https://doi.org/10.3390/photonics10121290 - 22 Nov 2023
Viewed by 1324
Abstract
Nondipole terms in the atom–laser interaction arising due to the presence of a magnetic component in an electromagnetic wave and its inhomogeneity lead to the nonseparability of the center-of-mass (CM) and electron variables in the neutral atom and, as a consequence, to its [...] Read more.
Nondipole terms in the atom–laser interaction arising due to the presence of a magnetic component in an electromagnetic wave and its inhomogeneity lead to the nonseparability of the center-of-mass (CM) and electron variables in the neutral atom and, as a consequence, to its acceleration. We investigate this effect and the accompanying excitation and ionization processes for the hydrogen atom in strong (1012 – 2×1014 W/cm2) linearly polarized short-wavelength (5 eV ≲ℏω≲ 27 eV) electromagnetic pulses of about 8 fs duration. The study was carried out within the framework of a hybrid quantum-quasiclassical approach in which the coupled time-dependent Schrödinger equation for an electron and the classical Hamilton equations for the CM of an atom were simultaneously integrated. Optimal conditions with respect to the frequency and intensity of the electromagnetic wave for the acceleration of atoms without their noticeable ionization were found in the analyzed region. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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11 pages, 2407 KiB  
Article
The Role of Collision Ionization of K-Shell Ions in Nonequilibrium Plasmas Produced by the Action of Super Strong, Ultrashort PW-Class Laser Pulses on Micron-Scale Argon Clusters with Intensity up to 5 × 1021 W/cm2
by Igor Yu. Skobelev, Sergey N. Ryazantsev, Roman K. Kulikov, Maksim V. Sedov, Evgeny D. Filippov, Sergey A. Pikuz, Takafumi Asai, Masato Kanasaki, Tomoya Yamauchi, Satoshi Jinno, Masato Ota, Syunsuke Egashira, Kentaro Sakai, Takumi Minami, Yuki Abe, Atsushi Tokiyasu, Hideki Kohri, Yasuhiro Kuramitsu, Youichi Sakawa, Yasuhiro Miyasaka, Kotaro Kondo, Akira Kon, Akito Sagisaka, Koichi Ogura, Alexander S. Pirozhkov, Masaki Kando, Hiromitsu Kiriyama, Tatiana A. Pikuz and Yuji Fukudaadd Show full author list remove Hide full author list
Photonics 2023, 10(11), 1250; https://doi.org/10.3390/photonics10111250 - 10 Nov 2023
Viewed by 1518
Abstract
The generation of highly charged ions in laser plasmas is usually associated with collisional ionization processes that occur in electron–ion collisions. An alternative ionization channel caused by tunnel ionization in an optical field is also capable of effectively producing highly charged ions with [...] Read more.
The generation of highly charged ions in laser plasmas is usually associated with collisional ionization processes that occur in electron–ion collisions. An alternative ionization channel caused by tunnel ionization in an optical field is also capable of effectively producing highly charged ions with ionization potentials of several kiloelectronvolts when the laser intensity q > 1020 W/cm2. It is challenging to clearly distinguish the impacts of the optical field and collisional ionizations on the evolution of the charge state of a nonequilibrium plasma produced by the interaction of high-intensity, ultrashort PW-class laser pulses with dense matter. In the present work, it is shown that the answer to this question can be obtained in some cases by observing the X-ray spectral lines caused by the transition of an electron into the K-shell of highly charged ions. The time-dependent calculations of plasma kinetics show that this is possible, for example, if sufficiently small clusters targets with low-density background gas are irradiated. In the case of Ar plasma, the limit of the cluster radius was estimated to be R0 = 0.1 μm. The calculation results for argon ions were compared with the results of the experiment at the J-KAREN-P laser facility at QST-KPSI. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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13 pages, 26978 KiB  
Article
Dichroism Effects in the Ionization of Polarized Atoms by Short Circularly Polarized Laser Pulses
by Alexei V. Meremianin and Nikolai L. Manakov
Photonics 2023, 10(11), 1235; https://doi.org/10.3390/photonics10111235 - 5 Nov 2023
Viewed by 1243
Abstract
The dichroism effects, i.e., asymmetries of the ionization probability with respect to the inversion of either the atomic orientation (magnetic dichroism, MD) or the circular polarization degree of the photon beam (circular dichroism, CD), are investigated using the time-dependent perturbation theory (PT). It [...] Read more.
The dichroism effects, i.e., asymmetries of the ionization probability with respect to the inversion of either the atomic orientation (magnetic dichroism, MD) or the circular polarization degree of the photon beam (circular dichroism, CD), are investigated using the time-dependent perturbation theory (PT). It is shown that the magnitude of these effects depends not only on the polarization states of the atom and laser pulse but also on the intensity and duration of the latter. We find that the CD can also be observed in the ionization of oriented initial bound states, which is impossible in long-pulse ionization. Predictions of our PT analysis are supported by the results obtained by numerical solutions of the time-dependent Schrödinger equation (TDSE) describing the ionization of the excited 2P-states of the hydrogen atom. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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11 pages, 618 KiB  
Article
Phase-Matching Gating for Isolated Attosecond Pulse Generation
by Vasily V. Strelkov and Margarita A. Khokhlova
Photonics 2023, 10(10), 1122; https://doi.org/10.3390/photonics10101122 - 6 Oct 2023
Cited by 3 | Viewed by 1531
Abstract
We investigate the production of an isolated attosecond pulse (IAP) via the phase-matching gating of high-harmonic generation with intense laser pulses. Our study is based on the integration of the propagation equation for the fundamental and generated fields with nonlinear polarisation found via [...] Read more.
We investigate the production of an isolated attosecond pulse (IAP) via the phase-matching gating of high-harmonic generation with intense laser pulses. Our study is based on the integration of the propagation equation for the fundamental and generated fields with nonlinear polarisation found via the numerical solution of the time-dependent Schrödinger equation. We study the XUV energy as a function of the propagation distance (or the medium density) and find that the onset of the IAP production corresponds to the change from linear to quadratic dependence of this energy on the propagation distance (or density). Finally, we show that the upper limit of the fundamental pulse duration for which IAP generation is feasible is defined by the temporal spreading of the fundamental pulse during the propagation. This nonlinear spreading is defined by the difference in the group velocities for the neutral and photoionised medium. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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13 pages, 2046 KiB  
Article
On Phase and Amplitude Extraction in Bichromatic Ionization: A Proposal
by Maria M. Popova, Alexei N. Grum-Grzhimailo and Elena V. Gryzlova
Photonics 2023, 10(10), 1069; https://doi.org/10.3390/photonics10101069 - 22 Sep 2023
Viewed by 1103
Abstract
In the paper we propose a method for characterizing VUV pulse(s) in a bichromatic ionization setup. The scheme is based on s-shell ionization by joint action of circularly polarized fundamental harmonic and linearly polarized second one. The advantage of the proposed approach [...] Read more.
In the paper we propose a method for characterizing VUV pulse(s) in a bichromatic ionization setup. The scheme is based on s-shell ionization by joint action of circularly polarized fundamental harmonic and linearly polarized second one. The advantage of the proposed approach is the existence of kinematic (geometrical) zeros of partial amplitudes which positions can be extracted with minimal number of theoretical (spectroscopic) assumptions and therefore they may serve as natural reference points in measuring the relative phase and amplitude of the harmonics. In the paper, we investigate a general possible geometry setup with more detailed consideration of the edge cases and present calculation and numerical stimulation for helium ionization as an illustrative example. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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12 pages, 3855 KiB  
Communication
Control of Spectral and Polarization Properties of Quasiunipolar Terahertz Pulses in Strongly Nonequilibrium Magnetized Plasma Channels
by Anna V. Bogatskaya, Ekaterina A. Volkova and Alexander M. Popov
Photonics 2023, 10(5), 585; https://doi.org/10.3390/photonics10050585 - 17 May 2023
Viewed by 1468
Abstract
The possibility to control both spectral and polarization properties of seed THz pulses in strongly nonequilibrium elongated magnetized plasma channels formed via intense UV femtosecond laser pulses in nitrogen (air) is analyzed. The physical mechanism of THz pulse control is based on cyclotron [...] Read more.
The possibility to control both spectral and polarization properties of seed THz pulses in strongly nonequilibrium elongated magnetized plasma channels formed via intense UV femtosecond laser pulses in nitrogen (air) is analyzed. The physical mechanism of THz pulse control is based on cyclotron resonance, which can strongly reconstruct electrodynamical plasma features and, in particular, its ability to amplify the radiation of different spectral bands and polarization states. In particular, the formation of quasiunipolar pulses with a non-zero electric area and a specific polarization state is discussed. This study is based on the self-consistent solution of the kinetic Boltzmann equation for the electron velocity distribution function (EVDF) in the plasma channel and the second-order wave equation for THz pulse propagation. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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10 pages, 2052 KiB  
Communication
Dynamics of Gas Ionization by Laser Pulses with Different Envelope Shapes
by Anna Emelina, Ivan Laryushin and Alexander Romanov
Photonics 2023, 10(5), 499; https://doi.org/10.3390/photonics10050499 - 26 Apr 2023
Cited by 1 | Viewed by 1611
Abstract
The properties of the dynamics of gas ionization under the action of femtosecond ionizing laser pulses with various envelope shapes are studied. It is shown that the duration of ionization in the saturation regime (at a high final degree of ionization) can either [...] Read more.
The properties of the dynamics of gas ionization under the action of femtosecond ionizing laser pulses with various envelope shapes are studied. It is shown that the duration of ionization in the saturation regime (at a high final degree of ionization) can either increase or decrease with an increase in the peak intensity of the ionizing pulse, depending on the shape of its envelope. We also determined the influence of the pulse shape on the spectrum of Brunel harmonics and the terahertz yield when two-color pulses are used. Full article
(This article belongs to the Special Issue Atomic and Molecular Processes in Strong Laser Fields)
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