Resonant field enhancement of terahertz waves in subwavelength plasmonic structures

Resonant terahertz field enhancement is investigated in arrays of subwavelength holes patterned on metals, semiconductors and superconductors. The effects of array film thickness, the dielectric function of metals, and a dielectric overlayer were investigated by the state-of-the-art terahertz spectroscopy. Extraordinary terahertz transmission was demonstrated in arrays of subwavelength holes made even from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth. We also demonstrate active control of surface plasmons at terahertz frequencies. Direct transitions of surface plasmon modes from a photonic crystal minimum or an inductive-capacitive metamaterial resonance in photo-doped semiconductor arrays are observed. In addition, we demonstrate a superconducting plasmonic array of subwavelength holes with active thermal control over the resonant transmission. Such plasmonic structures are promising in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy and integrated terahertz devices.