RESUMO
Intense laser fields interact very differently with micrometric rough surfaces than with flat objects. The interaction features high laser energy absorption and increased emission of MeV electrons, ions, and of hard x-rays. In this work, we irradiated isolated, translationally-symmetric objects in the form of micrometric Au bars. The interaction resulted in the emission of two forward-directed electron jets having a small opening angle, a narrow energy spread in the MeV range, and a positive angle to energy correlation. Our numerical simulations show that following ionization, those electrons that are pulled into vacuum near the object's edge, remain in-phase with the laser pulse for long enough so that the Lorentz force they experience drive them around the object's edge. After these electrons pass the object, they form attosecond duration bunches and interact with the laser field over large distances in vacuum in confined volumes that trap and accelerate them within a narrow range of momentum. The selectivity in energy of the interaction, its directionality, and the preservation of the attosecond duration of the electron bunches over large distances, offer new means for designing future laser-based light sources.
RESUMO
Using two-dimensional (2D) and three-dimensional (3D) kinetic simulations, we examine the impact of simulation dimensionality on the laser-driven electron acceleration and the emission of collimated γ-ray beams from hollow microchannel targets. We demonstrate that the dimensionality of the simulations considerably influences the results of electron acceleration and photon generation owing to the variation of laser phase velocity in different geometries. In a 3D simulation with a cylindrical geometry, the acceleration process of electrons terminates early due to the higher phase velocity of the propagating laser fields; in contrast, 2D simulations with planar geometry tend to have prolonged electron acceleration and thus produce much more energetic electrons. The photon beam generated in the 3D setup is found to be more diverged accompanied with a lower conversion efficiency. Our paper concludes that the 2D simulation can qualitatively reproduce the features in 3D simulation, but for quantitative evaluations and reliable predictions to facilitate experiment designs 3D modeling is strongly recommended.
RESUMO
We use 3D simulations to demonstrate that high-quality ultrarelativistic electron bunches can be generated on reflection of a twisted laser beam off a plasma mirror. The unique topology of the beam with a twist index |l|=1 creates an accelerating structure dominated by longitudinal laser electric and magnetic fields in the near-axis region. We show that the magnetic field is essential for creating a train of dense monoenergetic bunches. For a 6.8 PW laser, the energy reaches 1.6 GeV with a spread of 5.5%. The bunch duration is 320 as, its charge is 60 pC, and density is â¼10^{27} m^{-3}. The results are confirmed by an analytical model for the electron energy gain. These results enable development of novel laser-driven accelerators at multi-PW laser facilities.
