Superintense Femtosecond Laser Pulses Research Articles

Thermonuclear fusion in a strong laser field

Thermonuclear fusion induced by the irradiation of solid deuterated cluster targets and foils with fields of strong femtosecond and picosecond laser pulses is discussed. The thermonuclear-fusion process D(d, n)3He in a collision of two deuterons at an energy of 50 to 100 keV in a deuterium cluster target irradiated with a strong laser pulse is discussed. A theory of thermonuclear fusion proceeding upon the irradiation of clusters formed by deuterium iodide (DI) molecules with the field of a superintense femtosecond laser pulse is developed. This theory is based on an above-barrier process in which the sequential multiple inner ionization of atomic ions within a cluster is accompanied by field-induced outer ionization. The yield of neutrons from thermonuclear fusion in a deuteron-deuteron collision after the completion of a laser pulse is calculated. The yield of neutrons is determined for the thermonuclear-fusion reaction proceeding in the interaction of an intense picosecond laser pulse with thin TiD2 foils. A multiple ionization of titanium atoms at the front edge of the laser pulse is considered. The heating of free electron occurs in induced inverse bremsstrahlung in the process of electron scattering on multiply charged titanium ions. The yield of alpha particles in the thermonuclear-fusion reaction involving protons and 11B nuclei that is induced in microdrops by a strong laser field is determined. Experimental data on laser-induced thermonuclear fusion are discussed.

Features of femtosecond laser pulse reflection from a sharp boundary of relativistic laser plasma

The features of femtosecond laser pulse reflection from a plasma target of near-critical density were analytically and numerically studied in a wide range of laser pulse intensities and durations. Based on analytical calculations, it is shown that the pulse reflectance at a constant intensity decreases with decreasing pulse duration. Based of numerical simulation results, it is shown that, as a superintense femtosecond laser pulse is incident on a plasma layer with a concentration close to the critical one, a quasi-periodic electron-density structure is formed in the plasma bulk, which can both increase and decrease the the laser pulse reflectance.

Muon motion irradiated by a femtosecond laser pulse in muon-catalyzed fusion

Introducing a superintense femtosecond laser pulse in the muon-catalyzed fusion (μCF) target, taking the mixture after fusion reaction as a overdense plasma, and based on the Newton classical equations, the paper studies the movement of muon in the plasma. Muon drift along the direction of laser propagation remains even at the end of the laser pulse. At the peak laser intensity of 1021 W/cm2, muon goes from the skin layer into field-free matter in a short time much less than the pulse duration, before the laser pulse reaches its peak value. According to the calculated results, when the laser intensity reaches 1023 W/cm2, the relativistic muon drift should be considered. Influence of the laser on other particles in the plasma is small. Hence, this method can avoid muon sticking to alpha effectively and reduce muon-loss probability in μCF.

Recombination Processes in Laser Produced Dense Cluster Plasma

AbstractVarious mechanisms of recombination of electrons with multiply charged atomic ions in atomic clusters irradiated by superintense femtosecond laser pulses are discussed. Some of the recombination mechanisms are shown to take a time considerably longer than the laser pulse duration and, hence, they can develop only in a homogeneous, fairly rarefied cluster plasma after pulse termination. All autoionization states of multiply charged ions in a dense cluster plasma have been found to be destroyed by the Holtsmark electric field. Therefore dielectric recombination does not take place in irradiated clusters during the laser pulse. Only collision recombination electron ‐ ion ‐ electron occurs effectively in dense cluster plasma due to high charge multiplicity of produced atomic ions inside the cluster. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of fast multicharged heavy ions under the action of a superintense femtosecond laser pulse on the cleaned surface of a target

It is found that the mean charge of tungsten ions in a solid tungsten target cleaned from the surface layer of hydrocarbon and oxide compounds and exposed to femtosecond laser radiation with an intensity exceeding 1016 W/cm2 attains 22+, while the maximum charge is 29+. The maximum energy of such ions approaches 1 MeV. The corresponding values obtained on a dirty target with the same laser pulse parameters constitute 3+, 5+, and 150 keV. The results of numerical simulation show that such a large maximum charge of ions can be attained owing to the emergence of an electrostatic ambipolar field at the sharp boundary between the plasma and vacuum. The main mechanism of ionization of ions with maximum charges is apparently impact ionization in the presence of an external quasi-static field. In addition, direct above-threshold ionization by this field can also play a significant role. It is also shown that heavy ions in a clean target are accelerated by hot electrons. This leads to the formation of high-energy ions. The effect of recombination on the charge of the ions being detected is analyzed in detail.

Recombination processes in atomic clusters irradiated by superintense femtosecond laser pulses

Various mechanisms of recombination of electrons with multiply charged atomic ions in atomic clusters irradiated by superintense femtosecond laser pulses are discussed. All of the recombination mechanisms are shown to take a time considerably longer than the laser pulse duration and, hence, they can develop only in a homogeneous, fairly rarefied cluster plasma after pulse termination. All autoionization states of multiply charged ions in a dense cluster plasma have been found to be destroyed by the Holtsmark electric field.

Vacuum heating of large atomic clusters by a superintense femtosecond laser pulse

The analytic approach of vacuum (Brunel) heating mechanism is generalized to the case of large atomic clusters irradiated by a superintense femtosecond laser pulse. The hydrodynamic cluster expansion is taken into account in this approach. Simple universal expressions are obtained for the absorbed laser energy by a cluster and for the radius of an expanding cluster. The absorption of laser energy and the cluster expansion are determined by only one dimensionless field parameter.

Relativistic electron drift in overdense plasma produced by a superintense femtosecond laser pulse.

The general peculiarities of electron motion in the skin layer at the irradiation of overdense plasma by a superintense linearly polarized laser pulse of femtosecond duration are considered. The quiver electron energy is assumed to be a relativistic quantity. Relativistic electron drift along the propagation of laser radiation produced by a magnetic part of a laser field remains after the end of the laser pulse, unlike the relativistic drift of a free electron in underdense plasma. As a result, the penetration depth is much larger than the classical skin depth. The conclusion has been made that the drift velocity is a nonrelativistic quantity even at the peak laser intensity of 10(21) W/cm(2). The time at which an electron penetrates into field-free matter from the skin layer is much less than the pulse duration.

Generation of even harmonics in a relativistic laser plasma of atomic clusters

It is shown that the irradiation of atomic clusters by a superintense femtosecond laser pulse gives rise to various harmonics of the laser field. They arise as a result of elastic collisions of free electrons with atomic ions inside the clusters in the presence of the laser filed. The yield of even harmonics whose electromagnetic field is transverse is attributed to the relativism of the motion of electrons and the consideration of their drift velocity associated with the internal ionization of atoms and atomic ions of a cluster. These harmonics are emitted in the same direction as odd harmonics. The conductivities and electromagnetic fields of the harmonics are calculated. The generation efficiency of the harmonics slowly decreases as the harmonic number increases. The generation of even harmonics ceases when the drift velocity of electrons becomes equal to zero and only the oscillation velocity of electrons is nonzero. The results can also be applied to the irradiation of solid-state targets inside a skin layer.

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.

Weibel instability in plasma produced by a superintense femtosecond laser pulse

The Weibel instability increment is analytically derived for plasma produced at the barrier-suppression ionization of atoms and atomic ions by a superintense femtosecond laser pulse. The cases of linear and circular polarization are considered. Relativistic effects are discussed. It is found that the instability increment is larger for the circular polarization than for the linear polarization. This increment can attain the plasma frequency. Barrier-suppression ionization decreases the increment compared with the case of tunneling ionization. Relativistic effects also decrease the value of the increment. Estimates of the produced maximum quasistatic magnetic field are given.

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.

Observability of the dynamic stabilization of ground-state hydrogen with superintense femtosecond laser pulses

Theoretical information on dynamic stabilization (DS) of the ground state of H is still fragmentary, while its detection has remained open because of a lack of lasers with the required characteristics. The problem has been reactivated by the new light sources that are being developed, such as VUV-FEL's or attosecond pulses from high-harmonic generation, which will offer adequate frequencies, intensities, and pulse durations. We are now presenting a mapping out of DS over an extended range of high frequencies, for pulses with various envelopes, peak intensities, and durations. We find prominent DS under conditions where our nonrelativistic, dipole approximation, and calculation should be valid. There is a marked dependence of DS on the pulse shape. The effect of quasistationary stabilization (of the rates) on DS is analyzed. We comment on the impact of our results on the detection possibility. We conclude that ground-state DS for H should be observable with the new light sources in a state-of-the-art experiment.

X-Ray Production and Second Harmonic Generation by Superintense Femtosecond Laser Pulses in the Solids with Restricted Thermal Conduction

Two new types of targets: ultrathin freely suspended carbon films and porous Si, both revealing thermoconductivity restriction leading to plasma overheating upto electron temperature above 1 keV under "moderate" intensities 1015 - 1016 W · cm-2 has been investigated experimentally. For the ultrathin carbon film of 20–30 nm X-ray yield threefold increase has been observed. Computer simulations decribe well the observed behaviour of the X-ray yield, and the electron temperature of 700 eV was deducted for the film of 10 nm in thickness. Por-Si produces greater X-ray flux under intensity of 1016 W · cm-2 as compared to the solid Si. If the intensity increased the total X-ray yield from por-Si undergoes "saturation", while the X-ray yield from solid Si fits as ≈ I2. Simple model to describe the "overheating" of Si plasma using a set of ultrathin films is developed. Some promising advantages of new targets are discussed.