Mueller matrix study of the dichroism in nanorods dimers: rod separation effects.

We have studied the optical response of chiral metastructures composed of a disordered array of couples of plasmonic Au nanorods helically piled along the vertical direction. The fabrication is based on the use of multiaxial and multimaterial evaporation of the different metastructure building blocks through nanohole masks. From the analysis of the Mueller Matrix elements of the system, obtained both experimentally and from dedicated numerical simulations in forward and backward illumination conditions, we have been able to determine the linear and circular dichroic response of the system, as well as to sort out the optical anisotropy and intrinsic circular dichroism contributions to the circular differential extinction. We have also analyzed the dependence of the optical properties as a function of the angle between the rods and of the thickness of the dielectric separator. The study of quasi-planar as well as three-dimensional structures allows unraveling the role played by interactions between the constituting building blocks and, in particular, the distance between rods. We have experimentally and theoretically observed a decrease of the circular dichroic contribution and a change of the optical anisotropic contribution when the structures evolve from non-planar to planar.

Analysis and magnetic modulation of chiro-optical properties in anisotropic chiral and magneto-chiral plasmonic systems.

We present a systematic study to separate the different contributions to the dichroic response of complex plasmonic split-ring/ring magneto-chiral systems. For this, we first construct metastructures with plasmonic, chiral and magneto-optical functionalities by specific arrangements of different building blocks, each of them responsible for one of the functionalities. Then, by the use of Mueller matrices in forward/backward spectroscopic measurements under magnetic field, we separate optical anisotropy from pure chiral contributions to the overall dichroic response of the system. This allows determining the pure chiral response of the structures and the corresponding magnetic field modulation mediated by the magneto-optical effect present in the corresponding building block, which reaches values of 25% at 740 nm. This fabrication and characterization procedure, assigning the different optical functionalities to different building blocks, and decomposing the different contributions to the global optical response, allows an easy and rational identification of the different phenomena exhibited by the magneto-chiral system.