Tuning the Chirality of a Dipole Moment in an Achiral Particle with Structured Light

In the last decade, the attention drawn towards electric and magnetic dipole moments induced in optical nanoantennas significantly increased because of their numerous potential applications. For example, certain combinations of electric and magnetic dipoles allow for controlling the polarization state and propagation direction of light at the nanoscale. The underlying effects rely on specific orientations and phase relations between the individual electric and magnetic dipole moments. In a recent work, we presented a new addition to the toolbox of experimental nanophotonics, the so-called σ-dipole, consisting of parallel electric and magnetic dipole moments phase shifted by ±π/2. The name originates from its well-defined near- and far-field helicity of ±1. Utilizing a combination of in-phase radially and azimuthally polarized beams, tightly focused onto a silicon nanoparticle, a well-defined and controllable superposition of both σ-dipoles can be realized.