Ultrahigh-charge electron beams from laser-irradiated solid surface

Direct acceleration of collimated monoenergetic sub-femtosecond electron bunches driven by a radially polarized laser pulse

High-quality ultrashort electron beams have diverse applications in a variety of areas, such as 4D electron diffraction and microscopy, relativistic electron mirrors and ultrashort radiation sources. Direct laser acceleration (DLA) mechanism can produce electron beams with a large amount of charge (several to hundreds of nC), but the generated electron beams usually have large divergence and wide energy spread. Here, we propose a novel DLA scheme to generate high-quality ultrashort electron beams by irradiating a radially polarized laser pulse on a nanofiber. Since electrons are continuously squeezed transversely by the inward radial electric field force, the divergence angle gradually decreases as electrons transport stably with the laser pulse. The well-collimated electron bunches are effectively accelerated by the circularly-symmetric longitudinal electric field and the relative energy spread also gradually decreases. It is demonstrated by three-dimensional (3D) simulations that collimated monoenergetic electron bunches with 0.75° center divergence angle and 14% energy spread can be generated. An analytical model of electron acceleration is presented which interprets well by the 3D simulation results.

Research of Interaction between Ultra-Short Ultra-Intense Laser Pulses and Multiple Plasma Layers

In this research, we studied the interaction between the ultra-intense laser and multiple copper layers covered with multiple hydrogen layers. The research conditions are based on the symmetric and asymmetric structure of multilayer copper and hydrogen. It was found that the acceleration obtained from the first copper and hydrogen layer plasma was higher and occurred earlier than the second copper and hydrogen layer plasma. We investigated the spatial distribution and phase-space distribution of copper electrons, copper ions, hydrogen electrons, and hydrogen protons with different widths of the front hydrogen layer and the front copper layer, respectively. Theoretical simulations show that when the ultra-intense laser was irradiated in multiple copper layers coated with multiple hydrogen layers targets, some plasma phase-space distribution varied clearly in the different thicknesses of the first hydrogen layer or first copper layer, while some plasma were not influenced by the thickness of these two layers.

Hybrid stimulated Raman scattering-two-plasmon decay instability and 3/2 harmonic in steep-gradient femtosecond plasmas

We numerically study interaction of a very intense (I∼10^{17} to 5×10^{19}W/cm^{2}) femtosecond obliquely incident p-polarized laser pulse with a steep-gradient (L∼λ) plasma, i.e., within the conditions typical for modern experiments. It is shown that the hybrid stimulated Raman scattering-two-plasmon decay instability develops near the quarter-critical density surface and plays the dominant role for the plasma waves' excitation and energy absorption. The plasmons are excited as two wave packets confined near this surface with very wide ≈ω_{0}/c spatial spectra along its normal. Hence, phase-matching conditions for the 3/2 harmonic generation are fulfilled immediately and include the mechanism coming from the high harmonics of plasma waves. This mechanism has been proved experimentally by observing an additional 3/2 harmonic beam.

Production of Highly Polarized Positron Beams via Helicity Transfer from Polarized Electrons in a Strong Laser Field

The production of a highly polarized positron beam via nonlinear Breit-Wheeler processes during the interaction of an ultraintense circularly polarized laser pulse with a longitudinally spin-polarized ultrarelativistic electron beam is investigated theoretically. A new Monte Carlo method employing fully spin-resolved quantum probabilities is developed under the local constant field approximation to include three-dimensional polarization effects in strong laser fields. The produced positrons are longitudinally polarized through polarization transferred from the polarized electrons by the medium of high-energy photons. The polarization transfer efficiency can approach 100% for the energetic positrons moving at smaller deflection angles. This method simplifies the postselection procedure to generate high-quality positron beams in further applications. In a feasible scenario, a highly polarized (40%-65%), intense (10^{5}-10^{6}/bunch), collimated (5-70 mrad) positron beam can be obtained in a femtosecond timescale. The longitudinally polarized positron sources are desirable for applications in high-energy physics and material science.