Optical force enhancement and annular trapping by plasmonic toroidal resonance in a double-disk metastructure.

Optical forces can be enhanced by surface plasmon resonances with various interesting characteristics. Here, we numerically calculated the optical forces enhanced by a new kind of toroidal dipolar resonance in a double-disk metastructure. The results show that this kind of optical force is competitive with ordinary plasmonic forces and typically can reach-182.5pNμm²mW^-1. Influences of geometric parameters are discussed for the enhancement characteristic of optical force. Finally, we make a contrastive investigation on the optical trapping characteristic on a 5-nm-diameter nanoparticle, and show that the unique annular trapping region can be utilized for nanoscale applications.