Self distortion of an amplitude modulated electromagnetic beam in a plasma: Relaxation effects

Following a phenomenological approach an expression for the nonlinear current density in a plasma in the presence of an amplitude-modulated two-dimensional Gaussian (in space) electromagnetic beam has been derived. This expression has been used to study the nonstationary self focusing and resulting self distortion of the beam. The amplitude maxima/minima of the beam are focused by different amounts giving rise to a moving periodic focus and an overmodulation of the beam. The effect of finite values of relaxation times, involved in the nonlinearity, is to shift the amplitude envelope on the time scale.