Three regimes of intense laser beam propagation in plasmas

The nature of propagation of an intense laser beam in a plasma depends on the power and width of the beam and Ω, the ratio of plasma frequency and wave frequency. In this paper, for a given value of Ω (<1) three regimes have been obtained in the beam power-beam width plane, characterizing the nature of propagation as follows: (i) steady divergence (the beam keeps on diverging as it propagates in the plasma); (ii) oscillatory divergence (as the beam propagates in the plasma, the beamwidth oscillates between the original beamwidth and a maximum value); and (iii) self-focusing (as the beam propagates in the plasma the beam width oscillates between the original beam width and a minimum value). Ponderomotive force, collisions, and relativistic dependence of mass on quiver velocity have been considered to be the mechanisms of nonlinearity in the effective dielectric constant.