Optical activity in sub-wavelength metallic grids and fishnet metamaterials in the conical mount

We report on measurements of optical activity in reflection from plasmonic crystals consisting of a sub-wavelength silver meshed grid and a fishnet metamaterial in the conical mount. The fishnet metamaterials, formed by nano-imprint lithography, are the first large scale (cm2) samples that can be reliably investigated by plane-wave techniques with minimal focusing. For both materials we observe strong polarization conversion (s- to p-polarization, and vice versa) in generalized ellipsometry measurements when the measurement system is asymmetric. We compared the spectra to analytical predictions using surface plasmon polariton (SPP) theory and find good agreement for the meshed grid. The spectra for the meshed grid are also well modeled using the rigorous coupled wave analysis (RCWA) technique. Simulated results for the more complicated fishnet layer showing qualitative agreement are also presented. We then investigate the validity of describing the observations using homogenous parameters such as dichroism and birefringence, by examining the calculated reflection of nominally polarized incident light using simulated and measured Mueller matrices. The results show that the cross-polarization that we observe is primarily related to linear birefringence and dichroism, although circular effects are indeed present.