Near Field Surface Wave Enhanced Photon Transport

Radiative energy transfer as described by the classical radiation transfer theory of Planck is valid only when the distance between the participating surfaces is larger than a few wavelengths of the characteristic radiation. When the spacing is comparable to the wavelength, electromagnetic theory and the fluctuation-dissipation theorem can be used to predict the energy transfer between the surfaces. We have used the electromagnetic Green’s function method to model the thermal energy transfer between two half planes with planar layers in between. With polar materials as the half planes, we see a narrowband energy transfer in the near field due to energy transfer by surface phonon polaritons. We have used this technique to show that such a resonance, however dampened, persists even with the presence of a layer of photovoltaic material. This results in not only an increased energy transfer to the photovoltaic material as compared to black body radiation but also imparts a narrowband characteristic to it. The implications for thermophotovoltaics are discussed.