Resonant acceleration of electrons by intense circularly polarized Gaussian laser pulses

Resonant acceleration of plasma electrons in combined circularly polarized Gaussian laser fields and self-generated quasistatic fields has been investigated theoretically and numerically. The latter includes the radial quasistatic electric field, the azimuthal quasistatic magnetic field and the axial one. The resonant condition is theoretically given and numerically testified. The results show some of the resonant electrons are accelerated to velocities larger than the laser group velocity and thus gain high energy. For peak laser intensity I-0 = 1 x 10(20) W cm(-2) and plasma density n(0) = 0.1n(cr), the relativistic electron beam with energies increased from 207 MeV to 262 MeV with a relative energy width around 24% and extreme low beam divergence less than V has been obtained. The effect of laser intensity and plasma density on the final energy gain of resonant electrons is also investigated.