Transmission of light through slit apertures in metallic films

Transmission of polarized light through sub-wavelength slit apertures is studied based on the electromagnetic field distributions obtained in computer simulations. The results show the existence of a cutoff for E|| and a strong transmission (with no cutoff) for E?; here || and ? refer to the direction of the incident E-field relative to the long axis of the slit. These observations are explained by the standard waveguide theory involving inhomogeneous plane waves that bounce back and forth between the interior walls of the slit aperture. We examine the roles played by the slit-width, by the film thickness, and by the real and imaginary parts of the host material's dielectric constant in determining the transmission efficiency. We also show that the slit's sharp edges can be rounded to eliminate highly-localized electric dipoles without significantly affecting the slit's throughput. Finally, interference among the surface charges and currents induced in the vicinity of two adjacent slits is shown to result in enhanced transmission through both slits when the slits are separated by about one half of one wavelength.