  Optimally-chiral electromagnetic fields with maximized helicity density,
recently introduced in [1], enable chirality characterization of optically
small nanoparticles. Here, we demonstrate a technique to obtain
optimally-chiral nearfields that leads to the maximization of helicity density,
under the constraint of constant energy density, beyond the diffraction limit.
We show how optimally-chiral illumination induces balanced electric and
magnetic dipole moments in an achiral dielectric nanoantenna which leads to
generating optimally-chiral scattered and total nearfield. In particular, we
explore helicity and energy densities in nearfield of a spherical dielectric
nanoantenna illuminated by an optimally-chiral combination of azimuthally and
radially polarized beams that generates parallel induced electric and magnetic
dipole moments that in turn also generate optimally-chiral scattered field with
the same handedness of the incident field. The application of helicity
maximization to nearfields results in helicity enhancement at nanoscale which
is of great advantage in the detection of nanoscale chiral samples, microscopy,
and optical manipulation of chiral nanoparticles.
