  In addition to the ponderomotive acceleration of highly relativistic
electrons at interaction of very short and very intense laser pulses, a further
acceleration is derived from the interaction of these electron beams with the
spontaneous magnetic fields of about 100 MG. This additional acceleration is
the result of a laser-magnetic resonance acceleration (LMRA)[1] around the peak
of the azimuthal magnetic field. This causes the electrons to gain energy
within a laser period. Using a Gaussian laser pulse, the LMRA acceleration of
the electrons depends on the laser polarization. Since this is in the resonance
regime, the strong magnetic fields affect the electron acceleration
considerably. The mechanism results in good collimated high energetic electrons
propagating along the center axis of the laser beam as has been observed by
experiments and is reproduced by our numerical simulations.
