Experimental investigations of the role of proximity approximation in near-field radiative transfer

The nature of thermal radiative transfer changes significantly as the nominal gap between two objects becomes comparable to or smaller than the characteristic wavelength given by Wien's displacement law. At larger gaps, conventional theory of blackbody radiation is sufficient to describe the radiative transfer; at smaller gaps, however, wave effects such as evanescent wave tunneling, interference and diffraction render the classical theory invalid. The change in radiative transfer between two objects is most dramatic when they can support electromagnetic surface polaritons because of the high local density of states at the interface between the object and vacuum. When two objects of polar dielectric materials are close enough, the enhanced near-field radiation due to surface phonon polariton tunneling can exceed the blackbody limit by several orders of magnitude. This enhanced radiation at nanoscale has potential applications in energy transfer, heat assisted magnetic recording and near-field radiative cooling. In recent years, several experiments measuring the enhanced near-field radiation between a micro-sphere and a plane substrate have been reported. To measure the radiative tr