Enhancing Trace Terahertz Fingerprint Sensing by the Lossy Silicon Metagrating With a Gold Mirror

Dielectric metasurfaces typically have much lower terahertz (THz) optical losses than metallic metasurfaces and have attracted great attention in boosting trace sensing of THz molecular fingerprints. Previous studies usually neglect the losses of dielectric materials in their ideal physical models, and lack of experimental validation. Despite the low extinction coefficient of dielectric materials in metastructures, their optical losses cannot be neglected in practice, especially when their thicknesses are much larger than those of trace samples. This would hinder the retrieval of trace THz molecular fingerprints. In this work, we fabricate the THz dielectric metasurface of lossy silicon with a gold mirror and demonstrate its angle-multiplexed fingerprint metasensing scheme based on a series of guided mode resonances. We investigate the physical mechanism of silicon optical loss and mirror reflection. We discover that the use of a gold mirror in the lossy Si metastructure plays a critical role in boosting broadband THz fingerprint detection. Our method dramatically enhances the metasensing performance of the THz trace fingerprint, and the maximum enhancement is up to 98 times compared with conventional approaches. This article provides a powerful guide for the experimental study of trace THz fingerprint metasensing, which will inspire more THz trace sensing applications.