Extracting the anisotropic optical parameters of chiral plasmonic nanostructured thin films using generalized ellipsometry

Abstract

Using a commercial ellipsometer and analytical inversion, we show that both linear and circular birefringence-dichroism pairs can be extracted from a single generalized ellipsometry measurement, providing a complete description of the polarization properties of anisotropic chiral films, which is a distinct advantage over typical circular dichroism measurements. This is demonstrated by measuring the anisotropic optical parameters of post-like and helical composite Ti/Ag thin films fabricated by dynamic shadowing growth. These films are both chiral and highly aligned, and the measured linear and circular birefringence-dichroism pairs scale with the shape anisotropy and chirality. Furthermore, because the total polarization anisotropy is measured through generalized ellipsometry, we are able to determine that the polarization eigenstates can be effectively tuned from purely circular to approximately linear by changing the pitch number, N, of plasmonic helices for N≤1. © 2014 AIP Publishing LLC.