  Thermal fluctuations of charged particles, fluctuations akin to Brownian
motion, can excite optical surface-states leading to the concept of the thermal
near-field, which is a highly localized, and, therefore, evanescent optical
density of states that exist at distances much less than the thermal emission
wavelength. By tunneling the surface charge emitted photons into nearby
waveguides, the thermally excitable near-field optical density of states can be
enhanced, engineered, and efficiently extracted to the far-field for
observation. With this technique, the plasmonic thermal near-field of a 10nm
thick ITO film, known to have plasmonic activity in the 1500nm wavelength
region, was probed under external illumination and by thermal excitation at
873K. The results confirm that waveguides provide a large density of optical
channels with spatial overlap and k-vector matching to facilitate plasmon
de-excitation in the near-field through photon tunneling for extraction into
the far-field. Furthermore, it is shown that the thermal near-field can be
observed without the introduction of a vacuum-gap, a feature unique to this
particular method.
