OVERDENSE PROPAGATION OF A RELATIVISTICALLY INTENSE LASER-LIGHT

One-dimensional (1D) propagation of a relativistically intense circula rly polarized electromagnetic (EM) wave in an over-critical density pl asma is investigated. Cases of fast group velocity to which ions canno t follow the motion and of slow propagation in which ion dynamics play s an important role are discussed. However, electrons can be treated a s in static force balance keeping local charge neutrality. It is shown that plane waves are always unstable in the overdense plasma. In part icular, two types of modulational instability are found in the case of slow propagation and their growth rates are obtained. It is also show n that an envelope solitary wave solution can be obtained in an overde nse region. Density limit for the solitary wave propagation is obtaine d as a function of its amplitude. The solitary wave is a rarefaction w ave for the case of fast propagation, while it becomes of compressiona l character propagating with supersonic speed far the case of slow pro pagation. A general expression for the propagation speed as a function of the plasma density and the solitary wave amplitude is obtained for the compressional solitary wave. and the upper and lower limits of th e density (or the amplitude) for given amplitude (or density) are obta ined. A three-dimensional (3D) effect is briefly discussed and a bound ary value problem is formulated for the case in which the plasma fills a half space with the other half space being in vacuum. For the case of an EM wave with ultrarelativistic intensity the transmission coeffi cient into an over-critical density plasma is found to be a universal function of the ratio of the incident wave amplitude to the plasma den sity.