Optical chirality of vortex beams at the nanoscale.

In this work we undertake a systematic study of the optical chirality density of Laguerre-Gaussian and Bessel laser beams tightly focused into nanoscale volumes. In particular we highlight the unique contributions to optical chirality from longitudinal electromagnetic fields, i.e. light that is polarised in the direction of propagation. The influence that polarisation, spin and orbital angular momentum, radial index, degree of focusing, and diffraction has on the optical chirality is studied. The results show that the optical chirality of structured light beams at the nanoscale is significantly richer than that of the well-known circularly polarised propagating plane wave. The work lays the foundation for chiral nanophotonics, and chiral quantum optics based on structured light illumination.