Plasmonic Fabry-Pérot resonator for enhanced terahertz sensing

We report on studies of the plasmonic Fabry-P\'erot resonator, which features a metallic grid lithographically fabricated on both sides of a silicon substrate. It is found that the resonator effectively accumulates and enhances the electric field of the incident electromagnetic wave. We have managed to directly measure the field enhancement by placing a diode detector inside the resonator. A remarkable $\ifmmode\times\else\texttimes\fi{}45$ amplification in the detector responsivity is achieved in the terahertz frequency range. The observed effect contrasts with that occurring in a high-$Q$ Fabry-P\'erot resonator with/without resistive sidewalls, where there is no enhancement of the external electromagnetic field.