Engineered Near and Far Field Optical Response of Dielectric Nanospheroids using Focused Cylindrical Vector Beams

We compare by finite-difference time-domain method the near- and far-field optical properties of silicon nanospheroids under linear polarization (Gaussian beam), and azimuthally or radially focused cylindrical vector beams. We provide a python toolkit allowing FDTD simulations using those excitation sources in Meep open-source software. In addition to the well-known preferential excitation of specific electric or magnetic resonance modes as function of the excitation beam polarization, we show that shape anisotropy affects the resonance wavelength and the dipole orientation of the dipolar modes. Depending on the spheroid deformation axis with respect to the polarization, we also show that the electric dipole resonance can be split in two modes separated by an antiresonance identified as an anapole mode. Finally, we show that optical properties in both far- (scattering pattern) and near-field (electric and magnetic field hot spots) can be modified by switching the excitation polarization at a given wavelength and by choosing properly the spheroid shape and dimensions.