Lateral Shifts in Near-Field Thermal Radiation with Surface Phonon Polaritons

Abstract

It is well known that radiative heat transfer in the near field regime can be greatly enhanced because of photon tunneling, during which the classical radiation theory fails to predict the energy propagation direction. In the present article, we investigate the lateral shifts of energy pathways in near-field thermal radiation between two SiC plates separated by a vacuum gap. The energy streamline (ESL) method can be combined with fluctuational electrodynamics to trace the Poynting vector at a fixed parallel wavevector component β. The spectral energy flux exhibits nearly monochromatic enhancement with the excitation of surface phonon polaritons. In the spectral region important for radiative energy transfer, there exist considerable lateral shifts depending on the values of β. The range of β dominantly contributing to the spectral energy flux is identified for different wavelengths by examining the Poynting vector equation. With the use of ESLs, the effect of coupled surface polaritons on the lateral shift is also investigated. Furthermore, the lateral dimension for the SiC plates to be treated as infinitely extended is estimated based on the lateral shifts in the wavelength region that mostly contributes to the total energy flux.