Thermal radiation and near-field energy density of thin metallic films
Institut für Physik and Center of Interface Science, Carl von Ossietzky Universität, 26111 Oldenburg, Germany
Corresponding author: a firstname.lastname@example.org
Revised: 31 January 2007
Published online: 21 February 2007
We study the properties of thermal radiation emitted by a thin dielectric slab, employing the framework of macroscopic fluctuational electrodynamics. Particular emphasis is given to the analytical construction of the required dyadic Green's functions. Based on these, general expressions are derived for both the system's Poynting vector, describing the intensity of propagating radiation, and its energy density, containing contributions from non-propagating modes which dominate the near-field regime. An extensive discussion is then given for thin metal films. It is shown that the radiative intensity is maximized for a certain film thickness, due to Fabry-Perot-like multiple reflections inside the film. The dependence of the near-field energy density on the distance from the film's surface is governed by an interplay of several length scales, and characterized by different exponents in different regimes. In particular, this energy density remains finite even for arbitrarily thin films. This unexpected feature is associated with the film's low-frequency surface plasmon polariton. Our results also serve as reference for current near-field experiments which search for deviations from the macroscopic approach.
PACS: 44.40.+a – Thermal radiation / 78.66.-w – Optical properties of specific thin films / 05.40.-a – Fluctuation phenomena, random processes, noise, and Brownian motion / 41.20.Jb – Electromagnetic wave propagation; radiowave propagation
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2007