Limitations of paraxial approximation to model elec-tron acceleration by a laser pulse in vacuum in the presence of an axial magnetic field

Abstract

We model electron acceleration using paraxial approximation (PA) and seventh order correction description (O7) of a laser field in vacuum in the presence of an axial magnetic field. The effect of initial momentum, laser intensity, spot size, and initial position of electron on optimum value of magnetic field and electron energy for linearly and circularly polarized laser pulse has been investigated. We show that PA fails to obtain correct values of optimum magnetic field and electron energy. The amplitude of oscillations of the electron increases with time in the presence of axial magnetic field and PA fails to correctly take into account focusing and defocusing of laser and obtain correct results.