Spectroscopic Mueller matrix ellipsometry of a gap surface plasmon array at conical incidences

Spectroscopic Mueller matrix ellipsometry is used to study an array of rectangular Au patches on a SiO2 film backed by optically thick Au. The array supports resonances related to gap surface plasmons and Rayleigh anomalies, and these are mapped out by full rotation of the azimuthal angle of incidence. The finite element method is used to model the system, and it is found that the Ti adhesion layers at SiO2/Au interfaces used in the manufacture process must be included in the model for accurate results. We show how oxidation of the Ti layer beneath the Au patch causes the optical response to drift in time, and we demonstrate an extreme sensitivity of the Mueller matrix to the dimensions of the patch.