High-emissivity directional narrowband mid-infrared thermal emitter based on quasi-bound states in the continuum

In order to improve the utilizing efficiency of thermal radiation, a large amount of research on thermal emitters has focused on improving the Q value and directionality. Here, to further improve the utilizing efficiency, What webelieve to be a new strategy for high-emissivity directional narrowband mid-infrared thermal emitters is introduced by combining Fabry-Pérot and symmetry-protected quasi-bound states in the continuum inside a dielectric metamaterial consisting of a top-layer Ge grating and a YbF₃ film on a metal substrate. The high directionality and high emissivity of the thermal emitters are achieved because radiation Q factor monotonically decreases with increasing angle, whereas dissipation Q factor is angle- independent. Experimental results demonstrate that the emitter exhibits thermal emission at the wavelength of 7.028 µm with high Q factor (Q = 62.9) and high emissivity (ɛ=0.89) at the angle of 15°, and low emissivity (ɛ<0.4) outside the range of 6° to 24°. The proposed thermal emitter holds potential for practical applications in fields such as gas molecule detection and biosensing.