On the Behavior of Surface Plasmons at a Metallo-Dielectric Interface

In an attempt to shed additional light on the extraordinary transmission of an electromagnetic wave through a subwavelength aperture, we undertake a more detailed analysis of the canonical problem of the magnetic field of a line source located at a silver-dielectric interface at optical wavelengths. In particular, we present a closed-form asymptotic evaluation of the branch cut integral and show that the branch cut term initially decays as x^-1/2, where x is the distance between the source and the field point along the interface, but for larger distances, it falls off more rapidly as x^-3/2. We also address the effect on a surface plasmon of a tarnished silver substrate. Our analysis supports the extraordinary transmission surface plasmon electromagnetic interaction model, explains the origin of the so-called “creeping wave,” and shows that the tarnish layer has a significant damping effect on the surface plasmon polariton.