| The goal of this study is to investigate the physical mechanism of field enhancement in plasmonic subwavelength structures in the terahertz regime. Such plasmonic structures were fabricated by using microelectronic lithography technique. By using terahertz time-domain spectroscopy, the transmission or reflection properties of the plasmonic structures were systematically investigated. Numerical simulations were carried out to further verify the experimental studies. We demonstrated that the resonance enhancement through subwavelength plasmonic structures at terahertz frequencies is due to either surface plasmons excited along the interface of dielectric and metal or dipole localized surface plasmons introduced by dipole oscillation of metallic particles. Compared to subwavelength hole structures, the coaxial and multilayer complementary structures can approach even higher enhanced transmission, which is due to the coupling between dipole localized surface plasmon of the particles, surface plamons and localized surface plasmons of the holes. Such plasmonic crystals can be potentially applied in sensors, frequency selective elements, and near-field spectroscopy. |
