Polarization independent lattice-coupled terahertz toroidal excitation

Abstract

The toroidal dipole excitation is important for metamaterial research because of its low-loss attribute. In this study, we demonstrate numerically and experimentally, a unique toroidal metasurface that modulates a broad resonance into a sharp mode, independent of the polarization of the incident terahertz (THz) radiation, by coupling the inherent toroidal dipole excitation to the lattice mode of the metasurface. The advantage of polarization independence enables the excitation of ‘lattice-coupled toroidal mode’ for both the orthogonally polarized states of the incident THz radiation in the metasurface. The interaction of the two resonances results in the enhancement of the quality factor of the metasurface at the point of resonance matching. The surface current profile as well as multipole analysis of scattered powers by electric, magnetic, and toroidal dipoles confirm the domineering effect of toroidal dipole excitation for both the polarization states of incident THz radiation. Such a lattice-matched toroidal excitation-based device has the potential to impact the development of polarization-independent THz components for ultrasensitive sensors, lattice-enhanced equipment, and slow light devices for light–matter interaction.