Leaky Mode Propagation in a High Intensity Plasma Waveguide

Abstract

The finite thickness of the electron density barrier in the shock driven plasma waveguide1 (see Fig. 1 of paper Mode Properties of a High Intensity Plasma Waveguide, this conference) implies that formally, there are no bound modes (ie. no discrete spectrum of channel propagation wavenumbers) since all fields leak to some extent. For sufficiently large ΔNe and rm (where ΔNe = Ne(rm)-Ne(0) is the electron density difference between the peak and on-axis electron density and rm is the radius to the electron density peak), low order leaky waveforms are effectively indistinguishable from eigenmodes of a channel having Ne(r)= Nemax for r>rm (idealized channel). As an example of this, Fig. 1 compares leaky waveforms from a model channel (consistent with predictions of our laser-plasma hydrodynamics code1) to eigenmodes of the corresponding idealized channel. In this case, the field attenuation in the walls is sufficient to result in little tunneling or leakage of the lowest order p=0, m=0 mode (where p and m are radial and azimuthal mode indices). The p=1, m=0 mode, however, is sensitive to the finite barrier thickness in this case.