Electromagnetic wave propagation in the relativistic regime

An electromagnetic wave is expected to propagate through an overdense plasma, provided that its amplitude is large enough to bring the electron motion into the relativistic regime. We study this induced transparency by using 1D and 2D particle simulations. We find that large chaotic longitudinal electric fields are generated and strong plasma heating takes place during the propagation. This behavior is attributed to parametric instabilities. In order to support this interpretation, the modulational and Raman instabilities of a relativistic electromagnetic wave are studied analytically as well as with the help of particle simulations. In addition it is found that a finite width beam is strongly self focused during its propagation in a plasma layer.