Superintense Laser Research Articles

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.

X-ray study of microdroplet plasma formation under the action of superintense laser radiation

We have measured the X-ray emission spectra of a plasma generated by laser radiation with an intensity above 1019W/cm2 and a pulse duration of 30 fs acting upon an argon jet target with a large abundance of micron-sized clusters. The time variation of the X-ray yield from ions of various multiplicities, calculated within the framework of a nonstationary kinetic model, shows a good qualitative agreement with the experimental time-integrated spectrum.

Generation of high magnetic fields in an atomic plasma by irradiation with asuper-intense femtosecond laser pulse

Quasistatic magnetic fields have been derived for a plasma produced bythe multiple barrier-suppression ionization of atoms of solid surfaces, orclusters produced by a super-intense femtosecond laser pulse. The cases oflinear and circular polarizations are considered. It was found that theWeibel instability increment in the case of circular polarization is muchlarger than in the case of linear polarization. Above-barrier ionization andrelativistic effects reduce the rate of increase compared to tunnelling ionization.Collisions of electrons with atomic ions and other electrons are takeninto account. Electron–ion collisions stop the development of the Weibelinstability due to the alignment of longitudinal and transverse velocities.Estimates of the Weibel maximum quasistatic magnetic field are given.

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.

Production of ultracollimated bunches of multi-MeV electrons by 35 fs laser pulses propagating in exploding-foil plasmas

Very collimated bunches of high energy electrons have been produced by focusing super-intense femtosecond laser pulses in submillimeter under-dense plasmas. The density of the plasma, preformed with the laser exploding-foil technique, was mapped using Nomarski interferometry. The electron beam was fully characterized: up to 109 electrons per shot were accelerated, most of which in a beam of aperture below 10−3 sterad, with energies up to 40 MeV. These measurements, which are well modeled by three-dimensional numerical simulations, validate a reliable method to generate ultrashort and ultracollimated electron bunches.

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.

Generation of subcycle relativistic solitons by super intense laser pulses in plasmas

2D and 3D particle in cell simulations of the interaction of ultra-short, high-intensity laser pulses with inhomogeneous plasmas show the formation of long-lived electromagnetic solitons. These solitons consist of electron density depressions and intense electromagnetic field concentrations with a bigger amplitude and a lower frequency than those of the laser pulse. A significant portion of the electromagnetic energy is trapped in the form of solitons. Due to the plasma inhomogeneity, the solitons propagate toward the plasma–vacuum interface where they radiate away their energy in the form of bursts of low frequency electromagnetic radiation.

X-ray amplification by laser controlled coherent bremsstrahlung.

A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes. A thin solid layer or any other periodic atomic structure with limited dimensions is exposed to a short, superintense laser pulse. The electrons are extracted from the layer due to the extreme force and penetrate periodically through the ionic structure. Consequently, thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length. The small signal gain of the generated x-ray radiation exceeds that arising from the multiphoton Compton process in plasmas and is competitive with that in the leading x-ray free electron lasers.

The Evolution of Large Metal Clusters in a Super-Intense Laser Field

The evolution of large metal clusters is considered when the cluster is irradiated by a super-intense ultra-short laser pulse. The cluster excitation results from the interaction of the electron subsystem with the laser field. The electron temperature and the charge of the produced cluster ion are derived for this process. The optical density of the cluster plasma is found to be relatively low for resonant radiative transitions of multicharged atomic ions inside the cluster. Thus, the reabsorption of photons is inefficient in the cluster plasma. The optimal conditions are analyzed for the effective absorption of laser radiation by the metal cluster. It was found that a maximum of absorption was achieved for large sizes of the clusters.

Time-dependent electron-ion collision frequency at arbitrary laser intensity-temperature ratio.

In superintense laser beams collisional absorption exhibits a large amplitude modulation over a laser cycle. In this paper formulas for the time-dependent electron-ion collision frequency nu(ei)(t) are presented. On the basis of a ballistic interaction model we deduce an expression for nu(ei)(t) which holds for an arbitrary isotropic distribution function and arbitrary anharmonic oscillatory electron motion [Eq. (4)]. For a Maxwellian we present compact formulas for the various ratios v(os)(t)/v(th). It is shown that the strong time dependence over one laser cycle leads to the generation of intense odd harmonics. The cycle-averaged collision frequency nu(ei);(t) is compared with expressions derived from the more complex dielectric model. It is shown that the correct choice of cutoffs as a consequence of dynamical screening is essential.

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.

Proton and ion acceleration by an ultra-shortpulse sub Peta-watt laser in deformed double-layer thin foils

Proton and ion acceleration by sub Peta-watt laser radiation in overdense plasmas, especially for convex thin foils, is studied by 2D3V-PIC (Particle in Cell) numerical simulations. It is found that the target and pulse shape design is important for the acceleration of the charged particles. When a superintense laser pulse interacts with a thin slab of ablative overdense plasma formed by the pre-pulse of the laser, its pondermotive pressure blows all the electrons away from a finite diameter spot on the slab. Consequently, the absorption efficiency of the laser is larger than 50%, but ion acceleration efficiency is small in the case of the material composed of atoms of large mass number, for example, Al. When the surface of the target is coated with a rigid solid or clusters, ions are accelerated efficiently and gain energies as high as 100 MeV. If hydrogen is coated on the back of the thin Al foil, due to the Coulomb explosion of ions, protons are accelerated more efficiently than the hydrogen foil.

High density collimated beams of relativistic ions produced by petawatt laser pulses in plasmas

Under optimal interaction conditions ions can be accelerated up to relativistic energies by a petawatt laser pulse in both underdense and overdense plasmas. Two-dimensional particle in cell simulations show that the laser pulse drills a channel through an underdense plasma slab due to relativistic self-focusing. Both ions and electrons are accelerated in the head region of the channel. However, ion acceleration is more effective at the end of the slab. Here electrons from the channel expand in vacuum and are followed by the ions dragged by the Coulomb force arising from charge separation. A similar mechanism of ion acceleration occurs when a superintense laser pulse interacts with a thin slab of overdense plasma and the pulse ponderomotive pressure moves all the electrons away from a finite-diameter spot.

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.

Ultrahigh electron acceleration and Compton emission spectra in a superintense laser pulse and a uniform axial magnetic field

Exact expressions for the electron trajectory and energy are discussed, which predict very high acceleration, in vacuum, by a laser field and a uniform magnetic field. The laser field is modeled by a ${\mathrm{sin}}^{2}$ pulse and the initial electron motion, propagation of the laser pulse, and the magnetic field are all chosen in the same direction. An acceleration gradient in the TeV/m range within a very short travel distance of the electron is shown to be possible when a resonance condition is initially met. The acceleration and radiation properties are investigated using a recent analytic solution [F. H. M. Faisal and Y. I. Salamin, Phys. Rev. A 60, 2505 (1999)] of the corresponding relativistic equations of motion in the laboratory frame. The radiation losses are shown to remain small under the resonance condition and the associated weak emission spectra are found to be characterized by highly irregular line distributions.

Evolyutsiya bol'shikh klasterov pod deistviem ul'trakorotkogo sverkhmoshchnogo lazernogo impul'sa

Evolyutsiya bol'shikh klasterov pod deistviem ul'trakorotkogo sverkhmoshchnogo lazernogo impul'sa