Nonlinear processes during the interaction of a petawatt laser pulse with a plasma in the presence of an external magnetic field Original Research Article

It is shown that the propagation of a strong electromagnetic pulse in a plasma is described by the system of nonlinear equations, averaged over the fast time. The analytical solution of this system shows that the wake field amplitude reaches its maximum value when the pulse length is of the order of the plasma wave length. It decreases in a dense plasma because the ponderomotive force effect on plasma electrons is compensated by an electrostatic field arising from the charge separation in a plasma. In the presence of an external magnetic field the efficiency of excitation of electrostatic oscillations depends on the direction of wave propagation. It is found that upper and lower hybrid electrostatic modes become parametrically unstable when an external magnetic field exceeds the threshold value.