Control of chiral response in clustered nanoparticles through cluster geometry

Chiral materials have different response to right and left circular polarized light. This chiral response is generally very weak for most chiral molecules, but for nano-scale structures it could possibly be orders of... [ view full abstract ]

Chiral materials have different response to right and left circular polarized light. This chiral response is generally very weak for most chiral molecules, but for nano-scale structures it could possibly be orders of magnitude higher. Modern fabrication techniques for nano-materials allow to create such meta-materials where chirality is controlled via shape and geometry.
One known technique is structured thin films with helical nano-structures. However, even much simpler achiral structures such as arrangements of nano-spheres can produce a chiral behavior purely from geometrical properties of a three-dimensional arrangement together with incoming light beam. The optical response of such nano-cluster depends strongly on the particle material composition, arrangement geometry, location in the focal plane and and the incoming beam properties and polarization state.
Here, we employ the so-called T-matrix method, which is faster than finite element methods and allows us to consider more parameters, to investigate chiral responses of nano-engineered metamolecules. Using this method we analyze the chiral response in a two-dimensional cluster, made from three single nano-spheres of different sizes and materials. The resulting chirality is induced here either by the choice of cluster geometry or by the choice of material composition. We investigate both homogeneous  and heterogeneous (where one particle differs from the two remaining) clusters. As an effective measure we plot transmittance of right and left-handed circularly polarized light hitting the very center of a cluster. As an example, see figures, a material dependent chirality can be achieved.
Further numerical results will be reported and the optimal geometry to maximize chiral response in planar structures will be presented.