2-D FDTD modeling of the Extraordinary Optical Transmission Phenomenon through gold film containing a subwavelength single slit

This article presents a computational-analysis study of the enhanced optical transmission phenomenon found within a thin gold film surface, containing a single subwavelength 1-D slit. The central difference approximation and the Yee algorithm were implemented to discrete classical 2-D space-time Maxwell's Equations throughout the Finite-Difference Time-Domain method and Matlab® software. A single nanoslit air region pierced in gold thin films was lighted under normal modulated Gaussian $\mathbf{TM}_{\mathbf{z}}$ pulse at wavelength of 300 nm and with a unit amplitude. The computational domain in the xy plane was 1 $\mu\mathbf{m}\ \mathbf{x}\ 1\ \mu\mathbf{m}$ , and the time step was 5 fs. In this work were studied the behavior of the tangential electric field intensity values $\mathbf{E}_{\mathbf{z}}$ through a nanoslit, derived from the FDTD computational simulations for twelve different aspect ratios $\mathbf{R}=\mathbf{t}/\mathbf{d}$ . It was shown that the diameter d (120, 150 or 200 nm) and the depth t (50, 100, 200, and 300 nm) of the nanoslit are critical for the coupling of the $\mathbf{TM}_{\mathbf{z}}$ wave with localized surface plasmons, inside the nanoslit region. In general, it was observed that when diameter d decreases, the extraordinary optical transmission phenomenon does not occur within the nanocavity air region, due to influence of higher order evanescent modes.