Inverse Faraday effect and propagation of circularly polarized intense laser beams in plasmas

The magnetic field generation through inverse Faraday effect and its effects on the propagation of a circularly polarized light wave are studied in a self-consistent way for relativistic intensities. The following results are presented. (i) The magnetic field is produced by two sources, the circular motion of single electrons which produces plasma magnetization, and the inhomogeneity of both the electron density and light intensity which produces nonzero currents in the azimuthal direction. The magnetic field is calculated for various profiles of electron density and light intensity. (ii) For the case of a plane wave in a homogeneous plasma, the cutoff frequency is calculated as a function of light intensity, which is different from that without consideration of magnetic field generation. An ultra-intense magnetic field as large as hundreds of MG is obtainable in an overdense plasma where the wave can propagate owing to the induced transparency. (iii) The evolution equations for a laser beam of finite width are derived. Due to magnetic field generation, the critical power for self-focusing of the laser beam is reduced by a factor of (1+₏^2/^2) ^-1; the magnetic field tends to reduce the effect of the electron cavitation resulting from the transverse ponderomotive force. 1996 The American Physical Society.