Probing thermal radiation of single or a small number of plasmonic nano-antennas

The electromagnetic modes of a sub-wavelength sized antenna can be excited both optically and through thermal fluctuations. When dealing with individual or a small number of nano-antennas, highly sensitive techniques, such as thermal radiation scanning tunneling microscopy, and infrared spatial modulation spectroscopy, are required in order to extract the very weak emitted thermal radiation. Using these techniques, we have been able to characterize the thermal emission of a single pair of sub-λ metal-insulator-metal antennas separated by a nanometric gap. It is found that the various hybrid modes of a single antenna pair can be simultaneously excited by thermal fluctuations, an essentially incoherent process arising from fluctuating thermal currents. The effect of hybrid plasmonic modes on the resonant behavior of the considered antenna system may guide future efforts for realizing tunable optical and thermal structures made up of a small number of antennas, for various applications.