Enhanced coherency of thermal emission: Beyond the limitation imposed by delocalized surface waves

Is it possible to achieve thermal radiation excited by surface waves having a coherence length much larger than what one might anticipate from the behavior of surface waves on a flat interface? We demonstrate an extraordinary coherent thermal radiation from coupled resonant cavities; each of them supports standing wave surface polaritons. The coupling is implemented by surface standing waves between the cavities. As a result, the spatial coherence length is increased by an order of magnitude compared with that of delocalized surface waves.