Magnetic field generation by amplitude modulated laser pulse in a rippled plasma

The mechanism of a self-generated magnetic field by an amplitude modulated laser beam propagation through a rippled plasma is analyzed. The amplitude modulated laser beam exerts a ponderomotive force on plasma electrons, giving them oscillatory velocities at the modulation frequency. The oscillatory velocity couples with the electron density ripple and drives a nonlinear current. This nonlinear current generates a magnetic field. The magnetic field amplitude shows the resonant enhancement at the laser modulation frequency close to the electron plasma frequency, proportional to the ripple density and the laser intensity. In the relativistic case, it also scales directly with the electron plasma frequency and inversely proportional to the square of laser spot size and can approach the order of several hundred-kilogauss.