Principles and application progress of mid-infrared metasurfaces in imaging and detection (Invited)

The mid-infrared band contains two atmospheric windows as well as the molecular fingerprint region, and therefore has important applications in infrared imaging and detection. Conventional mid-infrared optics are expensive and need complicated fabrications limited by the material and processing technology in imaging. In terms of the detection, limited by the small molecular absorption cross-section, the sensitivity is extremely low and there is a great challenge for the trace chemical detection. Metasurfaces are two-dimensional arrays composed of artificial building blocks at the subwavelength scale. They have the characteristics of small size, easy integration and high degree of freedom, which may provide a new implementation scheme for manufacturing the low-cost, light-weight and integrated mid-infrared optical devices. Surface-enhanced infrared absorption can effectively enhance molecular vibration signals and improve the detection sensitivity. In this review, the mechanism of mid-infrared metasurfaces in electromagnetic wave regulation and the principals of mid-infrared detection applications are introduced. The research progress in the imaging and detection of mid-infrared metasurfaces is sorted out, including the polarization imaging, tunable and reconfigurable metasurfaces, other special functions and metasurface structures using gold, silver, aluminum, graphene, silicon, germanium and other materials based on plasmon or bound states in the continuum principles for the detection.