Type of the Paper (Article

The influence of the film thickness and the substrate’s refractive index on the surface mode 7 at the superstrate is an important study step that may help clearing some of the misunderstandings 8 surrounding their propagation mechanism. A single sub-wavelength slit perforating a thin metallic 9 film is among the simplest nanostructure capable of launching Surface Plasmon Polaritons on its 10 surrounding surface when excited by an incident field. Here, the impact of the substrate and the 11 film thickness on surface waves is investigated. When the thickness of the film is comparable to its 12 skin depth, SPP waves from the substrate penetrate the film and emerge from the superstrate, 13 creating a superposition of two SPP waves, that leads to a beat interference envelope with 14 well-defined loci which are the function of both the drive frequency and the dielectric constant of 15 the substrate/superstrate. As the film thickness is reduced to the SPP’s penetration depth, surface 16 waves from optically denser dielectric/metal interface would dominate, leading to volume 17 plasmons that propagate inside the film at optical frequencies. Interference of periodic volume 18 charge density with the incident field over the film creates charge bundles that are periodic in space 19 and time. 20