Herein we perform three-dimensional finite-difference time-domain calculations on an isolated micron
size slit in a thin gold film to study the behavior of confined electromagnetic fields for TM, TE, and
circular incident polarizations. It is found that the electric and magnetic fields exhibit well defined standing
wave patterns inside the slit. Moreover, the electric and magnetic fields are seen to be out of phase, and the
power flow through the slit is governed mainly by the magnetic field for TM polarization and the electric
field for TE and circular polarizations. To understand these results a theoretical modal expansion of the
fields in the presence of the slit is done. It is found that the standing wave patterns and dephasing can be
attributed to a superposition of propagating and evanescent waveguide modes.
Subwavelength hole arrays in metal films have the potential to exhibit narrow and high refractive index
(RI) sensitive transmission features. We have previously demonstrated that such features can arise from
the coupling between Wood anomalies (WAs) and surface Plasmon polaritons (SPPs) on opposite sides of
the metal film, the "WA-SPP" effect. Rigorous coupled-wave analysis (RCWA) calculations on a 2D model, which are shown to give WA-SPP features very similar to that of 3D Finite-Difference Time-
Domain (FDTD) calculations, are performed to determine how system parameters influence the strength of the WA-SPP effect. Herein we show that the optimum values for the film thickness and hole diameter are 45 and 175 nm, respectively.