Plasmonic Resonance toward Terahertz Perfect Absorbers

Metamaterial perfect absorbers have garnered significant interest with applications in sensing, imaging, and energy harnessing. Of particular interest are terahertz absorbers to overcome the weak terahertz response of natural materials. Here, we propose lossy plasmonic resonance in silicon-based annular microcavities for perfect terahertz absorption. This mechanism is in stark contrast to earlier demonstrations of conventional terahertz perfect absorbers that invoke Lorentzian electric and magnetic resonances. A fundamental cavity mode coupled to coaxial surface plasmon polaritons is responsible for the predicted exceptional absorption of -58 dB with a 90% absorption bandwidth of 30%. The performance is in agreement with experimental validation and consistent with critical coupling and resonance conditions. This specific cavity design possesses great thermal isolation and minimal electromagnetic coupling between unit cells. These unique features exclusive to the plasmonic cavity introduce a promising avenue for terahertz imaging with enhanced contrast, resolution, and sensitivity.