Analytic and numerical study of magnetic fields in the plasma wake of an intense laser pulse

Abstract

Magnetic field generation by a laser-induced wakefield is studied in two-dimensional (2D) planar geometry, both analytically and numerically via particle-in-cell (PIC) code simulations. Generally, the magnetic field in the wake is perpendicular to the 2D plane and can be separated into two components: one is independent of time and uniform in the longitudinal (laser propagation) direction; the other depends on time and varies longitudinally. The scaling of magnetic field strength changes from dIL2/dr⊥ at low light intensities to dIL/dr⊥ at high intensities, where IL is the laser intensity and r⊥ the transverse coordinate. Furthermore, the varying component changes from a periodic to a rather complicated structure and tends to increase with the distance from the pulse front. In addition to the quasistatic component, the magnetic field contains a transient component radiating at nearly twice the plasma frequency during the early stage of wakefield buildup. Phase velocities of the wakefield equal to and less than the vacuum speed of light are considered.