TRAPPING OF AN ELECTROMAGNETIC-WAVE BY THE BOUNDARY OF CREATED PLASMA

We discuss a new phenomenon of the electrodynamics of transient media, the trapping of electromagnetic radiation by the boundary of a transi ent plasma due to the conversion of the radiation into surface waves l ocalized at the boundary. Calculations are done for an initial plane w ave and for a beam of finite width in conditions where the boundary of the suddenly created (because of ionization) plasma half-space is per pendicular to the initial wavefront. Two frequency down-shifted surfac e waves traveling along the boundary in opposite directions are shown to be excited, as well as frequency up-shifted outgoing radiation and a time-independent mode in the form of a spatially inhomogeneous struc ture of de currents and a magnetic field within the plasma half-space. We study the associated kinematic, amplitude, and energy relations. F inally, we establish that the most efficient trapping (up to 40% in en ergy) can be achieved with the forward (with respect to the direction of the initial wave propagation) surface mode and that the trapping is accompanied by concentration of electromagnetic energy at the plasma boundary. (C) 1998 American Institute of Physics.