Highly coherent thermal emission obtained by plasmonic bandgap structures

We demonstrate an extraordinary quasimonochromatic thermal emission with high spatial coherence length $(lc>2400λ)$ and a quality factor $Q=2320$ at radiation frequencies that are much smaller than the plasma frequency of metal $(ω≪ωp)$⁠. This emission is achieved by forming a plasmonic bandgap, which is obtained by a periodic structure on a metallic surface. Such a structure modifies the dynamics of the surface wave and results in a van Hove singularity [Van Hove, Phys. Rev. 89, 1189 (1953)] in the spectral density of states while maintaining a large coherence length.