Seminars and Events
Coordinator: Alvaro Blanco
31 January 2017, 12:00 h. Sala de Seminarios, 182
Unveiling Natural Optical Activity of Disordered Media
F. A. Pinheiro
Instituto de Física, Universidade Federal do Rio de Janeiro, Brasil
The concept of chirality, introduced by Lord Kelvin in order to describe geometrical objects that cannot superimposed with their mirror image, is ubiquitous in the natural world. Despite substantial efforts to understand the optical properties of naturally occurring chiral media and to design artificial ones, disordered media remain an overlooked class of chiral systems. Since disordered systems lack centre and plane of mirror symmetry, they should exhibit natural optical activity. However, previous experimental evidence of natural optical activity in random media has never been attributed to the intrinsic chirality of a random system, but rather to alternative explanations, such as surface contamination by unwanted chiral substances.
Here, we demonstrate natural optical activity due to intrinsic geometric chirality in disordered, diffusive scattering systems, consisting of plasmonic resonators. We employ a microscopic electromagnetic wave transport theory, and derive an expression for the rotatory power and the spatial dichroism of a medium consisting of randomly distributed pointlike scatterers. By means of a systematic statistical analysis of natural optical activity in random media, we argue that the standard deviation of both rotatory power and spatial dichroism are strongly dependent on the density of scatterers and the scattering mean free path. We independently confirm our results by full-wave finite element simulations and show that disordered ensembles of plasmonic nanoparticles can exhibit dichroism more than an order of magnitude higher than in helical configurations with the same particle density.