Surface electromagnetic waves in lossy conductive media: tutorial

Abstract

It is commonly believed that electromagnetic waves cannot propagate in lossy conductive media and that they quickly decay inside such media over short length scales of the order of so-called skin depth. In this tutorial, I demonstrate that this common belief is incorrect if the conductive medium exhibits strong gradients of dielectric permittivity. In fact, surface electromagnetic waves in such gradient-permittivity lossy conductive media may have a propagating character, and the propagation length of such waves may be considerably longer than skin depth. Similar to surface plasmons, the wavelength of these waves may be considerably shorter than the light wavelength in free space, which may enable applications in super-resolution microscopy and nanolithography techniques. However, unlike plasmonics-based nanophotonic devices, which are typically built using a very limited number of low-loss optical materials, the newly found class of surface waves may be supported by a much broader range of lossy media. For example, such materials as graphite and silicon seem to be ideal in UV nanophotonics applications.