Helicity Density Enhancement in a Planar Array of Achiral High-Density Dielectric Nanoparticles.

We propose a way to enhance electromagnetic field's helicity density of a circularly polarized plane wave based on its interaction with a layer composed of a planar periodic array of resonant achiral high refractive index dielectric nanoparticles. The array generates a surface distribution of helicity density that everywhere has the same handedness of the exciting plane wave. Such a property is useful to interact with chiral samples like a layer of chiral molecules and can be used to improve chirality detection, paving the way to chirality detection with circular dichroism (CD) at surface level instead of in the bulk. Importantly, since the proposed array is composed of achiral inclusions it does not contribute by itself to the observed CD signal, and hence, it eliminates the need to separate the CD signal of the array and the chiral sample, in detecting the sample's chirality.