Superintense Laser Fields Research Articles

Dimensional scaling treatment of stability of atomic anions induced by superintense, high-frequency laser fields

We show that dimensional scaling, combined with the high-frequency Floquet theory, provides useful means to evaluate the stability of gas phase atomic anions in a superintense laser field. At the large-dimension limit (D-->infinity), in a suitably scaled space, electrons become localized along the polarization direction of the laser field. We find that calculations at large D are much simpler than D=3, yet yield similar results for the field strengths needed to bind an "extra" one or two electrons to H and He atoms. For both linearly and circularly polarized laser fields, the amplitude of quiver motion of the electrons correlates with the detachment energy. Despite large differences in scale, this correlation is qualitatively like that found between internuclear distances and dissociation energies of chemical bonds.

Frequency-dependent stabilization ofHe−by a superintense laser field

Using the alternative representation of time-dependent Hamiltonians that describe laser-driven systems [I. Gilary and N. Moiseyev, Phys. Rev. A 66, 063415 (2002)], we have performed calculations for the stability of He{sup -} in a superintense linearly polarized laser field. We estimated the laser parameters, amplitude, and frequency needed to stabilize He{sup -}. If we choose the laser frequency {omega}=5 eV, the laser intensity needed for stabilization is I{sup critical}=9.0x10{sup 15} W/cm{sup 2} and the maximal detachment energy is 1.0 eV. Our results show that high frequencies and large intensities are preferred for stabilizing multiply negative atomic ions in superintense laser fields.

Phase dependence in the ionization of atoms by intense one-cycle laser pulses within the Landau–Dykhne approximation

The phase sensitivity of the atomic ionization by intense one-cycle linearly polarized laser pulses is discussed within the analytic Landau–Dykhne approximation. The generalized Keldysh parameter is introduced for analysis of two regimes of ionization. In the case of super-intense laser field we found that ionization by cosine waveform pulse is much more effective than that by sine waveform pulse with the same energy in the pulse. This is a pure quantum destructive interference effect. Electron energy spectra and effective electron temperatures are also derived analytically for both waveform pulses.

Dynamic nuclear Stark shift in superintense laser fields

The direct interaction of superintense laser fields in the optical frequency domain with nuclei is studied. As main observable, we consider the nuclear dynamic (AC) Stark shift of low-lying nuclear states due to the off-resonant excitation by the laser field. We include the case of accelerated nuclei to be able to control the frequency and the intensity of the laser field in the nuclear rest frame over a wide range of parameters. We find that AC-Stark shifts of the same order as in typical quantum optical systems relative to the respective transition frequencies are feasible with state-of-the-art or near-future laser field intensities and moderate acceleration of the target nuclei. Along with this shift, but only at intensities above the critical field strength, we find laser-induced modifications to the proton root-mean-square radii and to the proton density distribution. We thus expect direct laser-nucleus interaction to become of relevance together with other super-intense light-matter interaction processes such as pair creation.

New stable multiply charged negative atomic ions in linearly polarized superintense laser fields

Singly charged negative atomic ions exist in the gas phase and are of fundamental importance in atomic and molecular physics. However, theoretical calculations and experimental results clearly exclude the existence of any stable doubly-negatively-charged atomic ion in the gas phase, only one electron can be added to a free atom in the gas phase. In this report, using the high-frequency Floquet theory, we predict that in a linear superintense laser field one can stabilize multiply charged negative atomic ions in the gas phase. We present self-consistent field calculations for the linear superintense laser fields needed to bind extra one and two electrons to form He-, He2-, and Li2-, with detachment energies dependent on the laser intensity and maximal values of 1.2, 0.12, and 0.13 eV, respectively. The fields and frequencies needed for binding extra electrons are within experimental reach. This method of stabilization is general and can be used to predict stability of larger multiply charged negative atomic ions.

Nuclear Quantum Optics with X-Ray Laser Pulses

The direct interaction of nuclei with superintense laser fields is studied. We show that present and upcoming high-frequency laser facilities, especially together with a moderate acceleration of the target nuclei to match photon and transition frequency, do allow for resonant laser-nucleus interaction. These direct interactions may be utilized for the model-independent optical measurement of nuclear properties such as the transition frequency and the dipole moment, thus opening the field of nuclear quantum optics. As an ultimate goal, one may hope that direct laser-nucleus interactions could become a versatile tool to enhance preparation, control, and detection in nuclear physics.

Molecules in intense laser fields: Beyond the dipole approximation

The time-dependent Schroedinger equation is solved for a Born-Oppenheimer (static nuclei) three-dimensional H{sub 2}{sup +} in super intense laser fields (I=4x10{sup 18}, 10{sup 19}, and 4x10{sup 19} W/cm{sup 2}) at wavelength {lambda}{sub L}=45 nm and 25 nm to assess the influence of nondipolar (magnetic) effects on high order harmonic generation spectra in molecules. It is found that even harmonics appear due to the magnetic field component direction perpendicular to the electric field polarization with intensities about two orders of magnitude less than the odd harmonics emitted along the electric field polarization. The even harmonics exhibit plateaus with cutoffs which exceed in intensity the odd harmonic plateaus and maximum energies predicted by semiclassical electron recollision models. Although the spectra are weak, the wavelength of the recollision electron in the maximum energy regions correspond to subatomic dimensions and the corresponding emitted photons have subnanometer wavelengths.

Very-high-order harmonic generation from Ar atoms andAr+ions in superintense pulsed laser fields: Anab initioself-interaction-free time-dependent density-functional approach

We present an ab initio nonpertubative investigation of the mechanisms responsible for the production of very-high-order harmonic generation (HHG) from Ar atoms and ${\mathrm{Ar}}^{+}$ ions by means of the self-interaction-free time-dependent density-functional theory recently developed. Further, by introducing an effective charge concept, we can study at which laser intensity the contribution to the high-energy HHG from ${\mathrm{Ar}}^{+}$ ions precede over the Ar atoms. Comparing the HHG behavior from Ar atoms and ${\mathrm{Ar}}^{+}$ ions in the superintense laser field, we conclude that the high-energy HHG observed in the recent experiment originated from the ionized Ar atoms.

Muonic molecules in superintense laser fields.

We study theoretically the ionization and dissociation of muonic molecular ions (e.g., dd mu) in superintense laser fields. We predict that the bond breaks by tunneling of the lightest ion through a bond-softened barrier at intensity I > or =10(21) W/cm(2). Ionization of the muonic atomic fragment occurs at much higher intensity I > or =6 x 10(22) W/cm(2). Since the field controls the ion trajectory after dissociation, it forces recollision of a approximately 10(5)-10(6) eV ion with the muonic atom. Recollision can trigger a nuclear reaction with sub-laser-cycle precision. In general, molecules can serve as precursors for laser control of nuclear processes.

Electron in one-dimensional symmetric and asymmetric double-well potentials under intense/superintense laser fields: A numerical study based on time-dependent Schrödinger equation

The responses of an electron moving in one-dimensional symmetric and asymmetric double-well oscillator (DWO) potentials respectively are analyzed under intense and superintense laser fields by numerically solving the time-dependent Schrödinger equation and evolving the systems for 96 fs at λ=1064 nm as well as different laser intensities. Emphasis is placed on the study of only those features which can arise from the response of a single system. A detailed investigation of multiphoton processes such as high harmonics generation and the energy spectrum (obtained by fast fourier transform of the autocorrelation function) is made. The applicability of these DWOs as model systems for the generation of attosecond pulses is examined. Furthermore, a comparison is made with atoms and molecules under similar conditions, thereby establishing a qualitative parallelism in the behavior of real atoms/molecules and these model DWO systems.

Multiphoton pair production by a highly charged ion in an intense laser field

We investigate electron–positron pair production in the process where the electron–positron vacuum is strongly affected by the collision of an ultrarelativistic nucleus with a super-intense plane-wave laser field. We use an approach which fully accounts for the interaction of the electron–positron vacuum with the laser field, while the treatment of the ion–vacuum interaction is restricted to the first-order of perturbation theory. We calculate the total production rate as a function of the ion energy and of the laser field intensity, respectively. Our results indicate that, with the help of the upcoming accelerator generation, in the near future the process under consideration might be observable for the first time.

Guest Editor's Preface: The S. Feliu Conference

This issue of Laser and Particle Beams contains 25 papers that were presented at the conference on “Matter in Super-Intense Laser Fields: Short Pulse, Superstrong Laser-Plasma Interactions,” held in S. Feliu de Guixols, Spain, from 29 September to 4 October 2001. Almost 100 scientists and young researchers (Ph.D. students and Post Docs) took part in this successful event, despite the terrible terrorist acts of September 11, 2001 in New York, which prevented many speakers from taking part, especially those coming from the United States.

Three-dimensional angulardistribution of harmonics radiated by an atom interacting with ashort high-frequency super-intense laser pulse

Radiation patterns of a three-dimensional hydrogen atominteracting with a high-frequency super-intense laser field arepresented. The laser-atom interaction is modelled without thedipole approximation, i.e. taking into account themagnetic-field component of the laser. Both linearly andcircularly polarized laser fields are considered. The structureof the radiation patterns is analysed. Among the results the appearance of even harmonics with veryhigh relative intensity, due to the magnetic field, in the caseof the linearly polarized field isparticularly relevant.

Nuclear Fusion Induced by Super-Intense Ultrashort Laser Pulses in Deuterium Cluster Plasma

An SiO 2 aerogel with absorbed deuterium is suggested as a target for the fusion reaction d + d → He 3 + n by a super-intense ultrashort laser pulse. The multiple inner ionization of oxygen and silicon atoms in the fibersof this fractal aerogel takes place in super-intense laser field. The Coulomb explosion of the deuterated aerogel skeleton propels deuterons up to kinetic energies of ten keV and higher. The neutron yield is estimated up to 10 5 neutrons per laser pulse during 500 ps if the peak intensity is 10 1 8 W/cm 2 and pulse duration is 35 fs.

Relativistic classical Monte Carlo simulations of stabilization of hydrogenlike ions in intense laser pulses

The relativistic classical dynamics of hydrogenlike ions is investigated numerically in the presence of intense high-frequency laser pulses of intensity well above ${10}^{16}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ and various pulse lengths up to several hundred cycles. With rising effective charge $Z,$ the stabilized electron dynamics is shown to be increasingly governed by the joint interplay of Coulomb attraction and Lorentz force in the laser-propagation direction, involving also so-called magnetic recollisions. With regard to the ionization behavior, the varying stabilization with increasing Z can be largely described by scaling the angular frequency and electric field strength by ${Z}^{2}$ and ${Z}^{3},$ respectively, however, clear signatures appear also due to the increased role of relativity. For long pulses and slowly entering the relativistic regime, the enhanced adiabaticity of the pulse turn-on has insufficient influence because the breakdown of stabilization due to the Lorentz force will still be stronger due to the dominating role of the necessarily increased interaction time with the superintense laser field.

Nuclear fusion induced by a super-intense ultrashort laser pulse in a deuterated glass aerogel

A SiO2 aerogel with absorbed deuterium is proposed as a target for the fusion reaction d + d → He3 + n induced by a superintense ultrashort laser pulse. The multiple inner ionization of oxygen and silicon atoms in the aerogel skeleton occurs in the superintense laser field. All the formed free electrons are heated and removed from the aerogel skeleton by the laser field at the front edge of the laser pulse. The subsequent Coulomb explosion of the deuterated charged aerogel skeleton propels the deuterium ions up to kinetic energies of ten keV and higher. The neutron yield is estimated at up to 105 neutrons per laser pulse for ∼200–500 ps if the peak intensity is 1018 W/cm2 and the pulse duration is 35 fs.

Stabilization window and attosecond pulse train production at atom ionization in superintense laser field

We present the results of numerical experiments on a two-dimensional model atom driven by a high-intense laser pulse. The electron wave-packet behavior is studied in a range of laser parameters corresponding to the dynamic stabilization regime. Wave packet localization in this regime with arbitrary laser polarizations is shown to manifest itself macroscopically by high-order harmonic production in the form of long trains of attosecond pulses. Calculations for the sub-relativistic regime of laser-atom interaction are carried out without making the dipole approximation in order to take into account the Lorentz force effect in wave packet evolution. The transition from polychotomy to the magnetic-field-induced drifting at very high laser intensities is documented which results in the electron delocalization. As a consequence, the intensity dependence of the atomic survival probability as well as that of the efficiency of high-order harmonic production possess a wide "stabilization window" followed by an abrupt drop because of the magnetic field effect.

Magnetically induced ionization and rescatterings in intense laser fields

The dynamics of a classical electron in the field of a nucleus and the electrical and magnetical components of a superintense laser field is investigated analytically. Particular emphasis is placed on the motion in the propagation direction of the laser field which is governed in a competitive manner by a laser induced drift away from the nucleus and an attractive Coulomb force towards it. In order to characterize the ionization and recombination/rescattering dynamics we develop an approximate mapping of the space and momentum coordinates in phase space each time the electron crosses the axis of the laser field propagation. For a certain fraction of the initial phase-space coordinates of the electron in the vicinity of the nucleus we find that the drift can be compensated for due to the attraction of the nucleus. A large number of substantial and almost periodic bursts of acceleration by the nucleus is then possible in the direction of propagation of the laser field. We evaluate the corresponding harmonic spectrum and explain the features deviating from those in the laser parameter regime where the magnetic-field component can be neglected.

Recent New Developments of Steady‐State and Time‐Dependent Density Functional Theories for the Treatment of Structure and Dynamics of Many‐Electron Atomic, Molecular, and Quantum Dot Systems

AbstractWe present a short account of recent new developments of density‐functional theory (DFT) for accurate and efficient treatments of the electronic structure and quantum dynamics of many‐electron systems. The conventional DFT calculations contain spurious self‐interaction energy and improper long‐range potential, preventing reliable description of the excited and resonance states. We present a new DFT with optimized effective potential (OEP) and self‐interaction‐correction (SIC) to overcome some of the major difficulties encountered in conventional DFT treatments using explicit energy functionals. The OEP‐SIC formalism uses only orbital‐independent single‐particle local potentials and is self‐interaction free, providing a theoretical framework for accurate description of the excited‐state properties and quantum dynamics. Several applications of the new procedure are presented, including: (a) the first successful DFT treatment of the atomic autoionizing resonances, (b) a relativistic extension of the OEP‐SIC formalism for the calculation of the atomic structure with results in good agreement with the experimental data across the periodic table (Z = 2–106), (c) electronic structure calculation of the ionization properties of molecules, and (d) the delicated “shell‐filling” electronic structure in quantum dots. Finally we present also new formulations of time‐dependent DFT for nonperturbative treatment of atomic and molecular multiphoton and nonlinear optical processes in intense and superintense laser fields. Both the time‐independent Floquet approach and the time‐dependent OEP‐SIC technique are introduced. Application of the time‐dependent DFT/OEP‐SIC procedure to the study of multiple high‐order harmonic generation processes in intense ultrashort pulsed laser fields is discussed in detail.

Relativistic free-electron dynamics and light-emission spectra in the simultaneous presence of a superintense laser field and a strong uniform magnetic field

We present exact analytic trajectories for a relativistic electron in the presence of an elliptically polarized superintense laser field and a strong uniform magnetic field. Also derived are expressions for the velocity components of the electron and for its energy as functions of the phase of the laser field as a parameter. The analytic trajectory solutions are illustrated by numerical calculations employing laser-field parameters and magnetic-field strengths currently available for laboratory experiments. The trajectory solutions are useful for (among other things) the study of the related problem of emission of radiation in the combined laser and magnetic fields. An exact expression for the cross section of light scattered by an electron initially moving along the laser propagation direction and in a magnetic field is given. It is found that, for observation along the common direction of laser propagation and the magnetic field, light at two frequencies $\ensuremath{\omega}={\ensuremath{\omega}}_{0}$ and ${\ensuremath{\Omega}}_{0}$ is scattered, where ${\ensuremath{\Omega}}_{0}={\ensuremath{\gamma}}_{0}(1+{\ensuremath{\beta}}_{0}){\ensuremath{\omega}}_{c},$ ${\ensuremath{\omega}}_{c}$ is the cyclotron frequency of the electron motion in the magnetic field, ${\ensuremath{\beta}}_{0}$ is the initial speed of the electron normalized by the speed of light, ${\ensuremath{\gamma}}_{0}=(1\ensuremath{-}{\ensuremath{\beta}}_{0}^{2}{)}^{\ensuremath{-}1/2}$, and ${\ensuremath{\omega}}_{0}$ is the laser frequency. Using the analytic solutions, we also study numerically the spectrum of radiation emitted along observation directions parallel to the electric and parallel to the magnetic components of the laser field. In each case, we present and discuss the dependence of the spectra on (a) the increase of the electron initial velocity, (b) the intensity and the frequency of the laser, and (c) the strength of the magnetic field.