Enhancing THz fingerprint detection on the planar surface of an inverted dielectric metagrating

Abstract

Terahertz (THz) molecular fingerprint sensing provides a powerful label-free tool for the detection of trace-amount samples. Due to the weak light–matter interaction, various metallic or dielectric metasurfaces have been adopted to enhance fingerprint absorbance signals. However, they suffer from strong background damping or complicated sample coating on patterned surfaces. Here, we propose an inverted dielectric metagrating and enhance the broadband THz fingerprint detection of trace analytes on a planar sensing surface. Enhancement of the broadband signal originates from the effects of evanescent waves at the planar interface, which are excited by multiplexed quasi-bound states in the continuum (quasi-BICs). One can evenly boost the near-field intensities within the analytes by tuning the asymmetry parameter of quasi-BIC modes. The multiplexing mechanism of broadband detection is demonstrated by manipulating the incident angle of excitation waves and thickness of the waveguide layer. Compared to the conventional approach, the THz fingerprint peak value is dramatically elevated, and the largest peak enhancement time is 330. Our work gives a promising way to facilitate the metasensing of the THz fingerprint on a planar surface and will inspire universal THz spectral analysis for trace analytes with different physical states or morphologies.