Extremely high Q-factor terahertz metasurface using reconstructive coherent mode resonance.

High Q-factor resonance has a pivotal role in wide applications for manipulating electromagnetic waves. However, high Q-factor resonance, especially in the terahertz (THz) regime, has been a challenge faced by plasmonic metamaterials due to the inherent ohmic and radiation losses. Here, we theoretically present a unique metasurface scheme to produce extremely high Q-factor Fano resonance of the reconstructive coherent mode in the THz regime. The THz metasurface is composed of periodically arranged vertical symmetric split ring resonators (SRRs), which can produce perfect reconstructive coherent coupling effect in the sense that dipole radiation is destructively suppressed. Under the polarized electric field perpendicular to SRR gap, the surface currents are out of phase for an individual SRR, leading to the cancellation of net dipole moment. The reconstructive coherent mode resonance can occur between each SRR and its neighboring SRRs, accompanied by destructive interference of the scattered fields of each SRR. This is due to the coupling between the localized resonance of individual particles and the Rayleigh anomaly of the array. The proposed metasurface can significantly suppress far-field radiation and perform an extremely high Q-factor beyond 10 level with large modulation depth in the THz region, which pushes the advancement of THz high Q-factor resonance. The extremely high Q-factor of reconstructive coherent mode is tunable by adjusting the geometry parameters. The design strategy is useful to develop ultra-sensitive sensors, narrow-band filters and strong interaction of field-matter in the THz regime.