Pulse Propagation in a Dispersive Medium with Moving Density Profile

Abstract

Space-time ray methods are developed and employed to obtain asymptotic solutions for pulse propagation in media with slow spatial and temporal inhomogeneities. Emphasis is placed on cold isotropic plasmas whose plasma frequency ωp has a space-time dependence of the form (z−Vt), thereby simulating ordered profile motion. Asymptotic results are constructed directly by the ray method, are related to those in a spatially inhomogeneous but temporally invariant plasma by the Lorentz transformation, and are also compared with an exact closed form solution for the special case of exponential variation of ωp(z − Vt). The presentation stresses physical attributes of the propagation process through extensive use of space-time ray diagrams and plane wave dispersion surfaces.