Circular dichroism induced by Fano resonances in planar chiral oligomers

We present a general theory of circular dichroism in planar chiral nanostructures with rotational symmetry. It is demonstrated, analytically, that the handedness of the incident field's polarization can control whether a nanostructure induces either absorption or scattering losses, even when the total optical loss (extinction) is polarization-independent. We show that this effect is a consequence of modal interference so that strong circular dichroism in absorption and scattering can be engineered by combining Fano resonances with planar chiral nanoparticle clusters. The energy imparted by circularly polarized light on chiral matter is known to depend on the handedness of light; an effect known as a circular dichroism. This study reveals that an analogous effect can be realized in two-dimensional, planar chiral, nanostructures through a form of circular dichroism in far-field radiation and near-field material absorption that originates from Fano-like modal interference.