NONLINEAR EVOLUTION OF ULTRASTRONG LASER-PULSES IN A PLASMA - NEW PHENOMENA OF MAGNETIC INTERACTION BETWEEN STRONG ELECTROMAGNETIC BEAMS

Results of numerical simulations and analytical description of the pro pagation of two-dimensional, short relativistically strong laser pulse s in an underdense plasma are presented. The relativistic self-focusin g and filamentation of a laser pulse are demonstrated. The influence o f asymmetry of the pulse shape is studied. It is shown that the mergin g of self-focusing channels occurs due to attraction of the electric c urrents produced by fast particle motion inside the channels. It is fo und that external magnetic fields can bend the channels. These effects extend the range of the self-focusing phenomena because they allow th e energy of several channels to accumulate in one channel. Pulses that are shorter than the plasma wave but with a transverse size larger th an the wavelength of the plasma wave excite the regular wake wave whos e electric field accelerates the charged particles. The specific struc ture of the wake plasma wave makes it possible for electromagnetic rad iation to be focused by this wave.