Measurement of Coherent Thermal Emission Due to Magnetic Polaritons in Subwavelength Microstructures

Spectral and directional control of thermal emission is critically important for applications such as space cooling and energy harvesting. The effect of magnetic polaritons (MPs) on spectral modulation has been analyzed in metallic grating structures with a dielectric spacer on a metallic film. It has been predicted that the spectral emission peaks exhibit omnidirectional characteristics when MPs are excited. The present work provides an experimental demonstration of coherent thermal emission from several microfabricated grating structures in the infrared region from room temperature to elevated temperatures. The emittance at elevated temperatures is directly measured using an emissometer, while the room-temperature emittance is indirectly obtained from the reflectance measurement. The rigorous coupled-wave analysis and an LC-circuit model are employed to elucidate the mechanisms of various resonant modes and their coupling effect, taking into consideration the temperature-dependent electron scattering rate of the metals.