Small-scale electron density and magnetic-field structures in the wake of an ultraintense laser pulse

We investigate the interaction of a high intensity ultrashort laser pulse with an underdense collisionless plasma in the regime where the Langmuir wake wave excited behind the laser pulse is loaded by fast particle beams, formed during the wake wave breaking. The beam loading causes the deterioration of the central part of the wake wave near the pulse axis, and the formation of bunches of sharply focalized ultrarelativistic electrons. The bunches of electrons generate a fast propagating magnetic field, which we interpret in terms of the magnetic component of the Lienard-Wiechert potential of a moving electric charge.