Resonant absorption by a magnetic plasma at a rippled critical surface

Abstract

When laser light is incident on a plasma, unstable filamentary structures may develop, producing a rippling of the critical surface. Such density ripples lead to resonant absorption of normally incident, p-polarized laser light. In order to compute the absorption coefficient, the eikonal approximation for the ray path is adopted and the standard results for oblique incidence (characterized by the value of the plasma dielectric constant at the cutoff frequency of the incident light) are applied. Explicit results are given for various angles of incidence and ripple scale lengths. A one-dimensional plasma in a nonuniform magnetic field is then considered. In agreement with published results, it is also shown that the laser light absorption is mainly dependent on the magnetic field value at cutoff. Finally, the effect of a rippled critical surface and a magnetic field of thermoelectric origin (∇n×∇T) are combined and the resulting absorption coefficient is computed. The results are given for various angles of incidence, ripple scale lengths, and ratios of the electronic cyclotron to plasma frequencies.