Abstract
We derived a general equation governing the spectra of electrostatic surface plasmons supported by a waveguide structure of two identical plasma slabs separated by a dielectric medium. The plasma slabs are parallel, homogeneous, and have finite thicknesses. The geometry under consideration supports two surface plasmon modes, which we investigated numerically for Polyethylene epsilon(d) = 2.25 and vacuum epsilon(d) = 1 as central regions. With vacuum as a central region, the two surface plasmon modes become coupled and merge into the well known single mode of quasi-static frequency omega = 0.707 omega(p). The surface plasmon modes in the presence of a Polyethylene are decoupled and remain nondegenerate over the whole range of kd. Therefore, the two plasmon modes propagate independent of each other with distinct quasi-static resonance frequencies, namely, a backward wave with omega = 0.707 omega(p) corresponding to a single plasma-vacuum interface and a forward wave with omega = omega(p)/root 3.5 = 0.55 omega(p) corresponding to a single plasma-dielectric interface. Increasing the central region width is found to introduce a delay in reaching the quasi-static resonance frequencies. The effect of collision is to down shift the mode frequencies for long wavelengths and also to down shift the quasi-static frequencies.