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

Abstract

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 quasiplanar 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.

Towards chiral acoustoplasmonics

“…The top bar has the same H and L , but the width is W2 = 65 nm. This asymmetry in the width is introduced to mimic the profiles obtained from actual lithographic procedures [ 17 ], [ 18 ], [ 19 ]. In addition, it would allow fine-tuning over the spectral positions of the two resonances.…”

Orientation dependence of optical activity in light scattering by nanoparticle clusters

“…16,48 For computational convenience, we model the nanorods as prolate spheroids, 49 using a fast and accurate T -matrix algorithm developed by our group; 50 other elongated shapes would produce qualitatively similar results. 51 Many studies have explored the strong chiroptical response displayed by such dimers, 52–55 with a characteristic bisignate lineshape around the dominant plasmon resonance of the nanorods. 22–25 This signature circular dichroism is reminiscent of exciton-coupling between chromophores, 56 and is well-described in the coupled-dipole approximation.…”

Orientation dependence of optical activity in light scattering by nanoparticle clusters

“…This is arguably the simplest chiral nanostructure composed of achiral particles: with spherical particles, a minimum of 4 spheres is required 16,48 . Many studies have explored the strong chiroptical response displayed by such dimers [49][50][51][52] , with a characteristic bisignate lineshape around the dominant plasmon resonance of the nanorods [22][23][24][25] . This signature circular dichroism is reminiscent of exciton-coupling between chromophores 53 , and is well-described in the coupled-dipole approximation.…”