Generation and regulation of electron vortices in an underdense plasma by Laguerre-Gaussian laser pulses

Abstract

An analytical model is presented to control the angular momentum of electrons by impinging Laguerre-Gaussian (LG) laser beam in an underdense warm plasma. During intense laser-plasma interaction, radiative effects of intense long laser pulses become important, which are analyzed under quasi-static approximation. It is shown that the spot size of the laser beam controls the depth of doughnut-shaped ion-channel created in the plasma. Due to inhomogeneity of plasma density, the nonlinear beating of two fast-time-scale laser fields results in the generation of slow-time-scale “dc” magnetic fields. These fields confine the fast electrons in relativistic laser channel and support their direct coupling with the lasers’ fields. Inside the doughnut-shaped channel, the electrons are found to execute transverse betatron oscillations. At resonance, the laser field efficiently transfers the energy and momentum to the plasma electrons which can be controlled by the lasers and plasma parameters. The angular momentum of the electrons is also found to be dependent on the magnitude of the quasi-static axial magnetic field. Moreover, regulation of the electron angular momentum can explore various interesting areas including coherent vortex beam generation via synchrotron radiation process.