Discrete dipole approximation simulation of optical vortex excited plasmonic properties of a partially capped core-shell nanostructure

In this study, interactions between optical vortex light and partially capped core-shell (PCCS) nanostructures simulated by a discrete dipole approximation (DDA) method are described. The plasmonic characteristics of the PCCS structure, in which a part of the surface of dielectric nanoparticles is covered with a metal cap, can be tuned by the core-shell ratio and the coverage condition. It was found that the topological charge and the polarization degree indicating the state of the optical vortex determine the resonance order, peak wavelength, direction and magnitude of optical torque of the excited pseudo-plasmon resonance of PCCS structures. It was also found that under certain incident conditions, higher-order resonance modes, such as hexapole and octupole modes are excited. Likewise, distorted resonance modes due to the asymmetry of the structure are excited. These plasmonic characteristics cannot be realized by scalar beam excitation, it becomes possible by an asymmetrical PCCS structure with optical vortex excitation.