Enhanced transmission through metallic subwavelength slits

We present FDTD calculations for transmission of electromagnetic waves through periodic arrays of slits in a metallic screen. The results show resonant, frequency dependent, transmittance peaks for subwavelength widths of the slits which can be up to a factor of ten with respect to those out of resonance. Although our conclusions agree with previous work by Lezec and Thio as regards both the magnitude of the enhancement and the lack of contribution of surface plasmon polaritons of the metal surface to this effect, we derive an interpretation from a theory that deals with emerging beam-Rayleigh anomalies of the grating, and with Fabry- Perot resonances of the perforated screen considered as an effective medium.