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 <i>Q</i> 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 <i>Q</i> factor monotonically decreases with increasing angle, whereas dissipation <i>Q</i> factor is angle- independent. Experimental results demonstrate that the emitter exhibits thermal emission at the wavelength of 7.028 µm with high <i>Q</i> factor (<i>Q </i>= 62.9) and high emissivity (<i>ɛ</i>=0.89) at the angle of 15°, and low emissivity (<i>ɛ</i><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.