Time-Harmonic Optical Chirality for Classification of Scatterers

We derive matrix expressions for the scattering, extinction and conversion of the chirality of light scattered by bodies characterized by a time-harmonic T-matrix. In analogy with conditions obtained from the conservation of energy, these quantities enable the classification of arbitrary scattering objects due to their full, i.e. either chiral or achiral, electromagnetic response. To this end, we put forward and determine the concepts of duality and breaking of duality symmetry, anti-duality, helicity-flipping, helicity annhiliation and the breaking of helicity annihilation. Different classes, like e.g. chiral and dual scatterers, are illustrated in this analysis with model examples of spherical or non-spherical shape. As for spheres, these concepts are analysed on considering non-Rayleigh dipolar dielectric particles of high refractive index, which, having a strong magnetic response to the incident wavefield, offer an excellent laboratory to test and interpret such changes in the chirality of the illumination. In addition, comparisons with existing experimental data are made.