IR-Mueller matrix ellipsometry of self-assembled nanopatterned gold grid polarizer

A gold nanowired grid polarizer is studied in the mid-IR range by means of spectroscopic Mueller matrix ellipsometry. This material is also an example of a so-called 2-dimensional hyperbolic metamaterial/metasurface, and produced by low-cost large area scalable manufacturing techniques. We present the IR spectroscopic Mueller matrix optical response of such sample for a full azimuthal rotation. It is observed strong in-plane anisotropy due to the gold wire grid. The main objective is to show a characterization methodology to reveal the complete polarimetric response over a large spectral range, providing information about the effective optical properties of the sample. Three different optical models are proposed that catch the main features of experimental data. The first one is based on the Rigorous Coupled-Wave Analysis (RCWA) assuming the profile of the sample to be periodic, second, a Generalized Effective Medium Approximation (G-EMA) assuming oriented gold ellipsoids aligned along the lines of the wire grid, and third, a biaxial dispersion model. Experimental data is compared with simulated data obtained from the three optical models and a comparative analysis between them is presented. The different models allow to retrieve information on the characteristic dimensions of the nanowires, and also to obtain the two in-plane components of the effective dielectric tensor of the nanostructured layer. The tensor component parallel to the nanowires shows a metallic response whereas the component perpendicular to them behaves as a transparent dielectric. Moreover, we have also shown that the nanowired grid behaves as a hyperbolic material.