Anomalous absorption of linearly polarized laser pulse in overdense plasma

Abstract

Anomalous absorption of an intense short laser pulse in overdense plasmas is analyzed. A diffusion equation describing the time evolution of the electron distribution function is derived. From the equation it is shown that the electron distribution function becomes anisotropic in the momentum space, which gives rise to the absorption of the energy. The diffusion is dominant in px direction rather than pz direction. In pz direction, however, the drift term is contained resulting for the longitudinal component of the J X B force, which has ben neglected but is important for the intense laser case. The absorption coefficient and skin depth is obtained for the ASE regime. The absorption coefficient increases in time starting from the well-known absorption coefficient for a lower intensity laser pulse.