Unusual thermal emission from a three-dimensional metallic photonic crystal

We report the observation of unusual thermal radiation at elevated temperatures (T=400-900K) from a three-dimensional metallic photonic-crystal composite that includes a micro-cavity. Upon thermal excitation by a heating element of a large heat-mass and a constant temperature (heat bath), its emissive power at resonant wavelengths exceeds a blackbody’s at nominally the same surface temperature. The possible explanations include, but are not limited to, angular concentration of light emission, slightly lower lattice-temperature for a reference blackbody and also a significant pumping of hot electrons at resonance such that our sample’s electron-temperature is higher than its latticetemperature.