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The generation and transport of fast electrons play an important role in intense laser interaction with dense plasma. Here, we experimentally study fast electron generation using a planar aluminum target obliquely irradiated at a large incident angle by an ultrashort high-temporal-contrast relativistic laser pulse. Simulations show that for near-relativistic laser intensities, s-polarized lasers above a certain energy threshold can generate energetic electrons () with a high yield, which is different from the case of low laser contrast. It is also shown that the most energetic electrons are emitted along the target's surface and accelerated to high energies. The key features of the acceleration regimes of lasers with different polarizations are also given. [ABSTRACT FROM AUTHOR]

Collision of intermediate-energy heavy ions is an important way to investigate the state of high-density nuclear matter and formation of quark gluon plasmas. In this paper, we demonstrate from two-dimensional particle-in-cell simulations that hundreds-GeV Au79+ ions can be generated by ultrashort ∼1022–24 W cm−2 lasers interacting with high-Z grain doped gas. Under extremely intense laser field, strong γ-ray radiation has resulted in massive laser energy loss, and the invoked radiation reaction trapping of electrons weakens the heavy ion acceleration. However, due to hole-boring acceleration and multi-body expansion acceleration of high-Z grains, the energy conversion efficiency from laser to heavy ions is still up to 32%. Our results might provide an effective routine to carry out the experimental explorations of heavy-ion collisions by using hundreds-petawatt laser facilities. [ABSTRACT FROM AUTHOR]

Two-dimensional particle-in-cell simulations show that when an intense picosecond laser pulse irradiates a target with steep but smooth density profile, the target protons can be accelerated to high energies with small divergence by a combination of target normal sheath acceleration and radiation pressure acceleration. The effects of plasma density profile on proton acceleration and collimation are investigated. In general, smaller(larger) density gradients lead to larger(smaller) self-generated azimuthal magnetic fields and smaller(larger) target-back electrostatic sheath fields, and thus proton beams with smaller(larger) divergence angle as well as cutoff energy. Accordingly, within limits, proton beams with desired peaked spectrum, energy, and divergence angle can be obtained by tailoring the target density profiles. It is also demonstrated that target tailoring can be achieved by having two suitable nanosecond lasers separately irradiating the front and back sides of a uniform plane slab. [ABSTRACT FROM AUTHOR]

Target-normal sheath acceleration (TNSA) of ions by >100-fs relativistic laser pulses irradiating a multichannel target consisting of a row of parallel long wires and a plane back foil is studied. Two-dimensional particle-in-cell simulations show that the laser light pulls out from the wires a large number of dense hot attosecond electron bunches, which are synergetically accelerated forward by the relativistic ponderomotive force of the laser as well as the longitudinal electric field of a transverse magnetic mode that is excited in the vacuum channels between the wires. These electrons are characterized by a distinct two-temperature energy spectrum, with the temperature of the more energetic electrons close to twice the ponderomotive potential energy. After penetrating through the foil, they induce behind its rear surface a sheath electric field that is both stronger and frontally more extended than that without the channels. As a result, the TNSA ions have much higher maximum energy and the laser-to-ion energy conversion efficiency is also much higher. It is found that a laser of intensity 1.37 × 1020 W/cm2, duration 165 fs, and energy 25.6 J can produce 85 MeV protons and 31 MeV/u carbon ions, at 30% laser-to-ion energy conversion efficiency. The effects of the channel size and laser polarization on the TNSA ions are also investigated. [ABSTRACT FROM AUTHOR]

The acceleration of protons in dense plastic foils irradiated by ultrahigh intensity laser pulses is simulated using a two-dimensional hybrid particle-in-cell scheme. For the chosen parameters of the overdense foils of densities ρ=0.2, 1, and 3 g/cm3 and of an ultrahigh intensity (2×1020 W/cm2) laser pulse, our simulations illustrate that a high-density target is favorable to high collimation of the target-normal-sheath acceleration protons but less energy for a short acceleration time (<100 fs). In particular, the difference of strong local heating of the carbon ion for different plasma densities is clearly observed at both the front and rear surfaces of thin solid targets, suggesting that the effect of the density and composition of the targets are also important for correctly simulating energetic ion generation in ultraintense laser-solid interactions. [ABSTRACT FROM AUTHOR]

Three-dimensional particle-in-cell simulations show that the anisotropic collapse of a plasma microshell by impact of two oppositely directed intense laser pulses can create at the center of the shell cavity a submicron-sized plasma of high density and temperature suitable for generating fusion neutrons. [ABSTRACT FROM AUTHOR]

A simple but comprehensive two-dimensional analytical model for the interaction of a normally incident short intense laser pulse with a solid-density plasma is proposed. Electron cavitation near the target surface by the laser ponderomotive force induces a strong local electrostatic charge-separation field. The cavitation makes possible mode conversion of the laser light into longitudinal electron oscillation at laser frequency, even for initial normal incidence of laser pulse. The intense charge-separation field in the cavity can significantly enhance the laser induced u×B electron oscillation at twice laser frequency to density levels even higher than that of the initial target. [ABSTRACT FROM AUTHOR]

It is shown that an intense laser pulse can be focused by a conical channel. This anomalous light focusing can be attributed to a hitherto ignored effect in nonlinear optics, namely that the boundary response depends on the light intensity: the inner cone surface is ionized and the laser pulse is in turn modified by the resulting boundary plasma. The interaction creates a new self-consistently evolving light-plasma boundary, which greatly reduces reflection and enhances forward propagation of the light pulse. The hollow cone can thus be used for attaining extremely high light intensities for applications in strongfield and high energy-density physics and other areas. [ABSTRACT FROM AUTHOR]

A simple analytical model for intense-laser interaction with low-density plasma is used to investigate the dependence of the wake structure on the laser parameters and the background plasma density. Many of the properties observed in the existing multidimensional particle-in-cell simulations are qualitatively recovered. [ABSTRACT FROM AUTHOR]

Energetic proton generation from thin foil targets by ultraintense laser pulse is investigated using two-dimensional particle-in-cell simulation. Foil targets with concave, flat, and convex front surfaces are considered. The maximum energy of the accelerated protons depends on the front-surface curvature, and the highest-energy protons are from the concave foil. The result can be attributed to an enhancement of the generation as well as concentration of the laser-driven hot electrons by the concave surface. [ABSTRACT FROM AUTHOR]

An alternative fast-ignition method is proposed involving the formation of a hot spot outside the precompressed fusion-fuel core by a series of shocks driven directly by the light pressure of laser pulses of increasing intensities. It is shown that a hot spot, which can be of different material from that of the fuel core, with temperature ∼10 keV and density ∼200 g/cm2, can be formed. Being an electrically neutral plasma, the hot spot can easily be sent into the fuel core. [ABSTRACT FROM AUTHOR]

An electron with an appropriate initial velocity injected into an oncoming, ultraintense circularly polarized laser pulse can execute a circular relativistic motion at the peak of the laser pulse. The circulating electron then radiates in the same manner as that in the storage ring of a conventional synchrotron source. Owing to the extremely small orbit radius, the laser-field synchrotron radiation thus generated can be a compact source of radiation pulses at short wavelength and short duration. [ABSTRACT FROM AUTHOR]

Electron acceleration from the interaction of an intense short-pulse laser with low density plasma is considered. The relation between direct electron acceleration within the laser pulse and that in the wake is investigated analytically. The magnitude and location of the ponderomotive-force-caused charge separation field with respect to that of the pulse determine the relative effectiveness of the two acceleration mechanisms. It is shown that there is an optimum condition for acceleration in the wake. Electron acceleration within the pulse dominates as the pulse becomes sufficiently short, and the latter directly drives and even traps the electrons. The latter can reach ultrahigh energies and can be extracted by impinging the pulse on a solid target. [ABSTRACT FROM AUTHOR]

Particle-in-cell simulation and analytical modeling demonstrate that the reflection of a single-cycle light pulse from a thin target can produce an ultrashort ultraintense electromagnetic field. [ABSTRACT FROM AUTHOR]

An analytical model based on the diffraction-induced transformation [A. E. Kaplan, J. Opt. Soc. Am. B 15, 951 (1998)] for an ultrashort subcycle laser pulse propagating in vacuum is considered. The pulse is initially Gaussian. To the lowest order of the diffraction angle its evolution satisfies Maxwell’s equations. The model is used to study the motion of charged particles in the pulse. It is shown that the delta-function representation is an excellent approximation of a subcycle pulse for studying charged-particle dynamics in subcycle pulse. [ABSTRACT FROM AUTHOR]

Generation of 1012 W/cm2 Smith-Purcell radiation in the infrared (5-20μm) regime from the interaction of high-density laser-produced MeV electrons is proposed. The electron bunch is produced by impinging an intense ultrashort laser pulse on a metallic target with a grated upper surface. Particle-in-cell simulation shows that the electron bunch can efficiently couple to the periodic structure through the quasistatic self-generated electric and magnetic fields there. An analytical model for predicting the dependence of the radiation intensity on the laser and grating parameters is also proposed. With appropriate laser and grating parameters, the proposed scheme provides a tunable source for intense radiation in the infrared regime. [ABSTRACT FROM AUTHOR]

Near-infrared radiation around 1000 nm generated from the interaction of a high-density MeV electron beam, obtained by impinging an intense ultrashort laser pulse on a solid target, with a metal grating is observed experimentally. Theoretical modeling and particle-in-cell simulation suggest that the radiation is caused by the Smith-Purcell mechanism. The results here indicate that tunable terahertz radiation with tens GV/m field strength can be achieved by using appropriate grating parameters. [ABSTRACT FROM AUTHOR]