Effect of Small Spacings on Radiative Transfer Between Two Dielectrics

Two phenomena which influence the energy transfer by thermal radiation between two solid dielectrics separated by a vacuum gap are described. For typical dielectric systems, it is shown that these coupled phenomena, which are termed wave interference and radiation tunneling, influence the radiative transfer to the extent that the classical Stefan-Boltzmann radiation law is inadequate to describe the net energy transfer. Since both phenomena are significant only when the distance of separation between the surfaces of the solids is of the same order of magnitude as the wavelength of the radiation, their effect is greatest when the spacing is small. However, the actual magnitude of the difference between the present treatment and the classical approach is a complicated function of the surface spacing, the refractive indexes of the solids, and the temperatures of the solids, and can be as large as an order of magnitude.