Electron acceleration using twisted laser wavefronts

Abstract

Using plasma mirror injection we demonstrate, both analytically and numerically, that a circularly polarized helical laser pulse can accelerate highly collimated dense bunches of electrons to several hundred MeV using currently available laser systems. The circular-polarized helical (Laguerre–Gaussian) beam has a unique field structure where the transverse fields have helix-like wave-fronts which tend to zero on-axis where, at focus, there are large on-axis longitudinal magnetic and electric fields. The acceleration of electrons by this type of laser pulse is analyzed as a function of radial mode number and it is shown that the radial mode number has a profound effect on electron acceleration close to the laser axis. Using three-dimensional particle-in-cell simulations a circular-polarized helical laser beam with power of 0.6 PW is shown to produce several dense attosecond bunches. The bunch nearest the peak of the laser envelope has an energy of 0.47 GeV with spread as narrow as 10%, a charge of 26 pC with duration of ∼ 400 as, and a very low divergence of 20 mrad. The confinement by longitudinal magnetic fields in the near-axis region allows the longitudinal electric fields to accelerate the electrons over a long period after the initial reflection. Both the longitudinal E and B fields are shown to be essential for electron acceleration in this scheme. This opens up new paths toward attosecond electron beams, or attosecond radiation, at many laser facilities around the world.

Electron pulse train accelerated by a linearly polarized Laguerre–Gaussian laser beam

“…An important conclusion from our study is that the key features that were previously reported for a CP-LG beam [40,41] are retained in the case of an LP-LG laser beam. It is likely that experimentally it will be easier to generate a high-power LP-LG beam than a high-power CP-LG beams.…”

“…The longitudinal electric field has the same dependence on x as the field of the CP-LG beam considered in Ref. [41]. For example, we have…”

“…The transverse field is plotted off-axis because it vanishes on the axis of the beam for the considered helical beam. The most striking feature compared to the CP-LG beam examined in [40,41] is the appearance of higher-order harmonics in E y . In contrast to E y , B has a more regular shape.…”

“…Following the notations of Ref. [41], we create a circularly-polarized transverse electric field by adding E z = iσE y , where σ = 1 produces a rightcircularly polarized wave and σ = −1 produces a left-circularly polarized wave. We take a pair of CP-LG beams: one with l = −1, σ = −1 and another one with l = −1, σ = 1.…”

Intense harmonic generation driven by a relativistic spatiotemporal vortex beam

“…Concurrent with the progress in high-power lasers [6,7] , the production of intense spatial vortex beams in the relativistic region (> 10 18 W cm −2 for a laser wavelength of ∼ 1 µm) has been theoretically proposed [8][9][10] and demonstrated in laboratories [11][12][13] . Such advanced light sources provide new possibilities for light-matter interactions, such as donut/twist wakefield acceleration [14][15][16] , attosecond electron bunch generation [17][18][19] , formation of a large magnetic field [20] , high harmonics generation (HHG) [12,21,22] , and the spin-orbital interaction [23][24][25][26][27] . In particular, the SAM and/or OAM of fundamental-frequency photons are transferred into high harmonics during HHG.…”