Mueller Matrix Spectroscopic Ellipsometry: Revealing Metasurface Functionalities

Metamaterials and metasurfaces rely on a combination of spatially arranged plasmonic meta-atoms and their phase effects in order to create novel optical functionalities. It is crucial to characterize such surfaces over the whole k-space and with large bandwidth in both amplitude and phase to capture their complete operation, especially when the structures present a three dimensional character. At optical frequencies, most of the investigations so far do not cover all these aspects. Here, we present Mueller matrix spectroscopic ellipsometry (MMSE) as a powerful characterization method for nanostructures, metamaterials and metasurfaces in the visible and near-infrared wavelength ranges. Along with transmission measurements to identify the modes at play, we perform MMSE on plasmonic metasurfaces to obtain phase information and reveal their extra-ordinary optical properties. We discuss results obtained from different types of metasurfaces - metallic wires, particle arrays, meanders, nanospirals - and show that the investigated samples exhibit a complex optical response that cannot be encompassed by effective material parameters. The role of the excited plasmonic modes and their coupling is very important to tailor the optical response of these structures. The discussion is based on experimentally measured Mueller matrix elements, their analysis and comparison with simulations. In particular parameters such as ellipticity and optical rotation can be extracted. For instance, large phase retardance and huge optical rotatory power, several orders of magnitude larger than that observed in conventional crystals, can be obtained for plasmonic meanders in spite of their nanometric character. The huge potential of such metasurfaces for optical applications is revealed. This study brings a novel understanding of the interaction of the plasmonic metasurfaces with polarized light, and opens the path for future designs with respect to plasmonic integration and creating of novel functionalities maintaining the compactness of the devices. Further, it is demonstrated that Mueller matrix spectroscopic ellipsometry is able to shed light onto the complex response of plasmonic nanostructures and opens the path for future designs of innovative optical devices.

audrey.berrier@pi1.physik.uni-stuttgart.de