Experimental observation of anomalous thermal radiation from a three-dimensional metallic photonic crystal.

We report some striking results on thermal radiation properties of a resonantly coupled cavity photonic crystal (PhC) at elevated temperatures (T = 400-900 K). We experimentally found that at resonant wavelengths, λ = 1.1, 1.64, 2.85 μm, the PhC emission is spectrally selective, quasi-coherent, directional, and shows significant deviation from Planck's blackbody law at equilibrium. The presence of non-equilibrium effects, driven by strong thermal excitation and cavity resonance, may be the major cause for our experimental observation.