This work deals with the optical properties of two types of layered composite materials containing metallic nanostructures which present multipolar plasmon resonances. Two methods were used to study the optical properties in the near IR-visible spectrum: finite elements model calculation and generalized ellipsometry. The first type of material contained an array of gold U-shaped resonators realized by e-beam lithography. Mueller-matrix measurements by ellipsometry allowed evidencing two special optical properties: on one hand a magneto-electric coupling and on the other hand spatial dispersion. We have built a parameterized optical model with permittivity, permeability and chirality constitutive tensors using Lorentz oscillators to describe the plasmon resonances effect. We have shown that this model allowed to fully describe layer's optical properties, together with the effects of spatial dispersion. The parameters of the model were adjusted so as to reproduce the measured Mueller matrices. The values of the parameters extracted from the adjustment agreed well with those obtained by finite elements method. The second type of material was an assembly of helical shape nanostructures made of silver. We calculated the optical response values using finite elements method, with a numerical sample including non idealities. The samples investigated showed a strong spatial dispersion; however, the calculated generalized ellipsometric spectra agreed well with measured ones. This hinted towards the presence of the resonant modes observed thanks to the simulation, into the real sample. These resonances could be employed in metamaterials design.
