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The radiation trapping effect (RTE) of electrons in the interaction of an ultra-intense laser and a near-critical-density plasma-filled gold cone is numerically investigated by using the particle-in-cell code EPOCH. It is found that, by using the cone, the threshold laser intensity for electron trapping can be significantly decreased. The trapped electrons located behind the laser front and confined near the laser axis oscillate significantly in the transverse direction and emit high-energy $\gamma $ photons in the forward direction. With parameters optimized, a narrow $\gamma $ photon angular distribution and a high-energy conversion efficiency from the laser to the $\gamma $ photons can be obtained. The proposed scheme may offer possibilities to demonstrate the RTE of electrons in experiments at approachable laser intensities and serve as a novel table-top $\gamma $ ray source.

A multiple-pump-pulses-stimulated Raman backscattering amplification (m-SRA) scheme is proposed and examined using 1D PIC simulations. Compared with the SRA using a single long pump pulse, higher energy conversion efficiency can be obtained with the same output laser intensity by employing the m-SRA scheme. Unwanted Raman forward scattering can be suppressed in the m-SRA case. Favorable pulse envelope and frequency characteristics of the seed pulse after amplification are obtained by using the m-SRA scheme. [ABSTRACT FROM AUTHOR]

Ionization-induced electron injection in a chirped laser pulse driven wakefield acceleration is investigated through particle-in-cell simulations. We find that negative (positive) chirp can longitudinally stretch (compress) laser pulse, and the wakefield amplitude can be enhanced regardless of the chirp sign. On the other hand, the rapid compression of a positively chirped pulse leads to the decrease of the wakefield potential difference, which breaks the ionization injection condition and consequent injection truncation occurs. The effective injection only lasts for a few hundred micrometers and the detailed injection length is determined by the chirp parameter. As a result, a highly tunable quasi-monoenergetic electron beam with narrow energy spread, hundreds of MeV central energy and tens of pC charge can be stably produced by this scheme. [ABSTRACT FROM AUTHOR]

By using three-dimensional particle-in-cell simulations, we investigate the dynamics of ultraintense Laguerre–Gaussian (LG) laser pulses interacting with a wire target. When a relativistic LG-mode laser pulse sweeps a wire target, annular electron bunches with attosecond duration are periodically dragged out of the left tip of the wire. Due to the radial laser electric field force exerted on the electrons, the annular bunches are tightly constrained near the target surface and steadily propagate along the wire. A strong return current is thus induced to satisfy the plasma neutralization condition. Once leaving from the right tip of the target, the electron emission angle gradually decreases and each hollow electron bunch is converged into an electron disc. Under the action of the longitudinal electric field, electrons are continuously accelerated to 100s MeV. At the same time, the laser angular momentum is transferred efficiently to the beam angular momentum (BAM) of the bunches. The structure of the dense short electron bunches is stable and keeps intact for more than 300 fs. We can manipulate the quality of the bunches by changing the laser and target parameters, such as the laser handedness and intensity, beam waist radius, wire length and radius. The scheme paves the way for the generation of high-quality attosecond electron bunches with low divergence, high beam charge and large BAM, which will have wide-range applications in various domains. [ABSTRACT FROM AUTHOR]

Electron–positron pair production at ultra-relativistic laser intensities has been one of the most interesting topics of high energy physics and plasma physics in the last several decades. Here we report simulations of copious electron–positron pair production via enhanced electron injection from a mass-limited foil driven by a circularly-polarized laser pulse focused to the forthcoming intensity of 1023 W cm–2. The laser pressure pushes the center foil forward as a whole with the lateral laser wave passing by the foil boundary and being reflected by the second thick carbon target. The accelerated electrons from the mass-limited foil are injected into the reflected laser wave in the hole-boring front of the carbon target, resulting in a significant enhancement of the γ-photon emission via nonlinear Compton scattering. Finally, we obtain 1014γ-photons with an average energy of 14.48 MeV and a conversion efficiency from the laser to the γ-ray energy of 18%. A dense beam of 1011 positrons is produced with an average energy of 160 MeV, which may have wide-range applications to astrophysics and fundamental physics. [ABSTRACT FROM AUTHOR]