Adiabatic frequency shifting of a surface wave guided by a time-varying plasma structure

The propagation of an electromagnetic wave along a planar waveguiding structure that contains gaseous/solid-state plasma slabs with time-varying free carrier density is considered in the case when the time scale of the density variation is much greater than the wave period (adiabatic approximation). Both ionization and deionization (recombination, attachment) processes are included. General relations describing frequency shifting and energy losses of a guided wave are derived for an arbitrary open/closed waveguiding structure. Relations between the energy of the wave and its frequency conserved during the process of plasma density variation (adiabatic invariants) are found. Detailed analyses are given for surface waves guided by the boundary of a time-varying plasma half-space and a plasma slab. Slow variations of plasma density are shown to be energetically more efficient than fast variations. A new effect of reflection of the wave envelope that occurs without reflection of the fast oscillating carrier is pointed out. (C) 2000 American Institute of Physics. [S1070-664X(00)01703-1].