Highly-efficient gas sensing using dielectric-based narrow-band thermal emitters operating in the mid-infrared

Thermal emissions from nonlocal metasurface structures by harnessing the extended modes of bound states in the continuum (BIC) or quasi guided modes have the advantage of ultra-narrow bandwidth, which outperform their metallic metamaterial-based counterparts and enable many important applications in various fields. In this work, we present the results of gas sensing application by employing a narrow-band mid-infrared thermal emitter which is composed of a zigzag array of Ge elliptical disks separated from a gold substrate by an Al2O3 buffer layer. The well-known quasi-BIC response from the zigzag array of Ge disks allows the generation of the thermal emission with an experimentally demonstrated bandwidth of 53 nm. By designing the metasurface geometry to provide thermal emissions spectrally matching the absorption resonance of CO2 at 4.23 μm, our results based on the direct absorption measurement and Beer-Lambert law show that a CO2 detection with the concentration down to 40 ppm in the atmospheric environment can be achieved. This research provides a direct proof of high-performance gas sensing applications in the mid-infrared with narrow-band thermal emitters based on dielectric resonators.