Mid-infrared thermal emission from coupled surface plasmon-phonon polariton resonances

Strong coupling of infrared light and surface polarized ions provides a unique channel between photon and phonon via electric charge oscillations, which enables bidirectional energy flow between optical and thermal energy. Therefore, optical metasurfaces based on phonon polaritons are promising candidate as thermal metasurfaces according to Kirchhoff’s law of thermal radiation stating that the absorptivity of a resonator is equal to the emissivity. For a synchronized emission, resonators have crosstalk each other. We observe a well-defined and narrow-band thermal emission from coupled surface plasmon-phonon polariton resonance induced by deeply subwavelength-scale resonant nanocavity arrays. Metal (gold)-insulator (silicon) layered nanocavity on polar dielectric crystal (silicon carbide) confines a guided mode of coupled surface plasmon-phonon polaritons with half-wave Fabry-Perot resonance condition. Each cavity has a crosstalk with near neighbor cavities. We develop a mid-infrared grating spectrometer integrated into infrared microscope with Fourier transform infrared spectrometer. The filtered thermal emission by two spectrometers is observed while heating the sample up to 400 K. Our thermal emitter platform will benefit to design thermal metasurfaces.