Non-zero helicity extinction in light scattered from achiral (or chiral) small particles located at points of null incident helicity density

Abstract: Based on a recent unified formulation on dichorism and extinction of helicity on scattering by a small particle, dipolar in the wide sense, magnetodielectric or not, chiral or achiral, we show that such extinction is enhanced not only at resonances of the polarizabilities, but also due to interference between left and right circularly polarized components of the incident wave, which contributes with appropriate parameters of the illuminating field, even if the particle is achiral and is placed at points of the incident field at which the local incident helicity density is zero. This phenomenon goes beyond standard circular dichroism (CD), and we analyze it in detail on account of the values of the several quantities, both of the incident light and the particle, involved in the process. In addition, this interference produces a term in the helicity extinction that remarkably yields information on the real parts of the electric and/or magnetic polarizabilities, which are not provided by CD, of which that helicity extinction phenomenon may be considered a generalization.