Dynamics of wave-pulse penetration into an evanescent region.

Abstract

The initial problem of plasma wave dynamics in the presence of a sharp density jump that divides the space into transparent and opaque regions is studied. A wave packet is assumed to be initially localized in the transparent region. The transient process of field penetration beyond the density barrier during the wave packet reflection from the density jump is investigated. Signal velocity beyond the barrier is defined as the speed at which some small, but finite, value of the field amplitude appears in the evanescent region. This velocity, which is proved to be always less than the speed of light, is determined analytically for the case of quasi-Gaussian wave packet. Further insight into the field dynamics in opaque region is gained by considering a steplike initial wave packet.