The propagation of electromagnetic power through subwavelength slits in a metallic grating

The electric and magnetic field distribution in a 2D metallic grating containing small slits are determined with the aid of the rigorous coupled wave method. The streamlines of the time-averaged Poynting vector visualizing the propagation of net power are displayed for both the surface-plasmon-polariton (SPP) and waveguide mode (WGM) resonances identified earlier by Porto et al, [Phys, Rev. Lett. 83 (1999) 2845]. It is shown that both the streamline patterns and the stored energy distributions faithfully mirror the different physical mechanisms of the two resonances. The salient features of the power flow for the SPP case are shown to be well reproduced by a simple approximate formulation based on one propagating and two evanescent waves. (C) 2002 Elsevier Science B.V. All rights reserved.