Dispersion of surface plasmon polaritons on short-pitch metal gratings

The dispersion of surface plasmon polaritons (SPPs) has been calculated for short-pitch metal gratings for various depths. For gratings with depths greater than their pitch very flat SPP bands are formed in the zero-order region of the spectrum which may be resonantly excited with radiation polarized with its electric field in the plane of incidence of the radiation, which also contains the grating vector. The dispersion curves of these modes evolve as deformations of the familiar shallow grating dispersion curve due to the opening of very large band gaps, and interactions of the SPP bands with both the light line and other SPP bands. Also presented are the dispersion curves for the equivalent modes excited by radiation having its plane of incidence perpendicular to the grating vector, but polarized with its electric field parallel to this grating vector. The full dispersion curve of these SPP bands for all orientations of the grating relative to the plane of incidence is also presented.