Asymmetric scattering of mirror symmetric radiation from nanostructures coupled to chiral films

TL;DR

This paper demonstrates that nanostructures on chiral films can produce asymmetric scattering of mirror symmetric radiation, revealing new insights into mirror symmetry breaking in nanophotonics with potential applications in enantiomeric discrimination.

Contribution

It provides the first proof of asymmetric scattering from nanostructures on chiral films, highlighting the role of evanescent coupling and near-field effects in symmetry breaking.

Findings

Asymmetric far-field interference due to molecular chirality

Angular dissymmetry factor can reach tenths

Efficient enantiomeric discrimination schemes

Abstract

The interaction of radiation with chiral molecular films is not macroscopically invariant under mirror reflections and, accordingly, chiroptical effects exist which affect the spatial symmetry of the radiation profile and which nearly exclusively show up in the near-field due to the large molecule-wavelength size mismatch. Here we prove that the scattering of a mirror symmetric pair of plane waves by a nanowire lying on a chiral nanofilm is not mirror symmetric with an angular dissymmetry factor that can be as large as some tenths. Due to evanescent coupling, the nanowire efficiently experiences molecular chirality which produces a spatially asymmetric near-field so that the self-consistent unbalanced excitation of nanowire photonic modes with opposite angular momenta yields asymmetric far-field interference. In addition to enriching the physical understaning of mirror symmetry breaking in chiral nanophotonics, our results could suggest ultra-efficient schemes for enantiomeric discrimination which is essential in biological chemistry and pharmacology.