Resonant absorption in a parabolic density profile

The resonant absorption of an Electromagnetic Wave (EMW) in an inhomogeneous plasma is relevant to the physics of laser-matter interaction, ionospheric heating experiments and microwave laboratory experiments. Electrostatic Plasma Waves (EPW) are excited at the resonance location, where the local plasma frequency, ωp(x)/2π equals the incident wave frequency, ω0/2π, by an obliquely incident EMW with the electric field in the plane of incidence. When the amplitude of the EPW is increased, nonlinear effects appear: the ponderomotive force arising from the resonance EPW leads o a low-frequency density modulation, which in turn modifies the EPW propagation. This phenomenon is studied experimentally in a parabolic density profile ne(x) = nM(1-x2/l2) l is the half-width of the density profile. The critical density n0 is defined by ω02 n0 e2/ε0 me and characterized by β = nM/n0. The Zakharov equations are used to model the EPW propagation coupled with Ion Acoustic Waves through the ponderomotive force. (author). 7 refs, 3 figs