Studies On Terahertz Spectroscopy Of Superconducting Metamaterials And Subwavelength Hole Array

Terahertz (THz) metamaterials and plasmonics open the new path for the manipulation of THz wave and novel THz devices. The low loss and tunability of superconductors at THz frequencies make them suitable for fabricating THz functional devices. In this dissertation, the THz spectra of superconducting metamaterials and subwavelength hole array has been studied. The main contents in this dissertation are classified as follows:1.The frequency tuning and loss property of superconducting NbN THz metamaterials with resonance frequency above and below the gap frequency have been studied. It has been found that the relative tuning range is the widest as the resonance frequency approaches gap frequency. The Ohmic loss of NbN metamaterials is persistently low when the frequency is below gap frequency, and the unloaded quality factor is much higher than metamaterials made from normal metal. The transmission coefficient is well fitted into the framework of BCS theory and equivalent circuit model.2.The superconducting electromagnetic induced transparency metamaterials have been studied. Using the low loss property of superconductor and the strong interaction between two resonators, we realized high group delay-bandwidth product. Meanwhile, the transmission coefficient and group delay at transparency window is tunable. By applying two dark resonators with different resonance frequencies coupled with a radiative resonator, we realized the planar metamaterials mimicking four-level EIT system. Besides that, the spectral response of superconductor and metal-superconductor hybrid metamaterials was contrasted, and the effect of quality factor of resonators in slowing light has been discussed.3.The extraordinary optical transmission on superconducting NbN subwavelength hole array at THz frequencies has been studied. It has been found that the transmission peak is remarkably enhanced in superconducting state and the resonance frequency is temperature dependent, and this property was studied using Fano model and equivalent circuit model. The THz pulse time domain spectra were used to study the dynamic process of extraordinary optical transmission. The rigorous coupled mode analysis method has been used to simulate extraordinary optical transmission spectra. Furthermore, the extraordinary optical transmission phenomenon on high temperature superconductor subwavelength hole array has been studied, and the transmission peak arised from Josephson plasmonic oscillation has been investigated.