Mechanisms underlying extraordinary transmission enhancement in subwavelength hole arrays

Extraordinary transmission in subwavelength hole arrays has been interpreted by surface-plasmon models and diffraction-based models. To understand controversial mechanisms of transmission enhancement, we simulate hole arrays, using a rigorous Fourier-space scattering matrix simulation. At the enhanced transmission maximum there are large evanescent diffracted fields above the metal surface. These evanescent fields are decomposed into longitudinal and transverse components. Both components are comparable in magnitude. The longitudinal field is 15%-20% larger in the square lattice. Transverse fields are slightly larger in the triangular lattice. The longitudinal and transverse evanescent surface fields are related to bound surface modes of the hole array.