Improving the Radiation Efficiency of Terahertz Photoconductive Antenna with Hierarchical Spoof Plasmonic Structures

To improve the output power of the Photoconductive Antenna (PCA), one of the most widely used radiation sources of the Terahertz time-domain spectroscopy system, a design scheme for PCA based on hierarchical spoof plasmonic structures is proposed. Hierarchical structures are composed of the golden nanorod array and periodic micro-gratings. The theory and simulation results show that the golden nanorod array achieves near-field enhancement and photon-electron conversion efficiency improvement through spoof localized surface plasmon resonance effect, and the periodic micro-gratings improve vertical directivity of PCA by suppressing horizontal leakage with the forbidden band of the fundamental spoof surface plasmon polariton mode. Numerical calculation results further validate that compared with the unmodified PCA, hierarchical spoof plasmonic structures achieve vertical radiation power density improvement of PCA in a relatively broad band from 0.86 to 1.51 THz.