3D-FDTD Modeling of Angular Spread for the Extraordinary Transmission Spectra of Metal Films with Arrays of Subwavelength Holes

Extraordinary transmission through a metal film with an array of subwavelength holes (mesh) can be modeled effectively using three-dimensional finite difference time domain (3D-FDTD) calculations. A simple 3DFDTD model, where a plane wave of light at perpendicular incidence with no angular spread interacts with a periodic repeating mesh, models the shape and location of the transmission resonance peaks qualitatively but not quantitatively. The simple 3D-FDTD model gives peaks that are tall, sharp, and red-shifted compared to experimental measurements using a benchtop Fourier transform infrared (FTIR) spectrometer. It was discovered that the simple model does not account accurately for diffraction order scattering by the mesh or the angular spread of the actual FTIR beam. This work describes a more sophisticated model that accounts for these factors and agrees quantitatively with experimental FTIR results.