Structured light finds many interesting applications in numerous fields, such as information encoding, wavefront manipulation and imaging. The opportunity to engineer the field distributions of optical beams opens up many exciting possibilities for achieving new optical interactions with materials and molecules. In this work we theoretically and experimentally investigate the interaction of cylindrical vortex beams (CVBs) with a strongly anisotropic plasmonic metamaterial, focusing on the case of radially and azimuthally polarised beams. We developed a semi-analytical model to describe the propagation of CVBs through an anisotropic slab, describing the metamaterial by means of an effective medium theory. In the tight focusing regime, the extinction properties of the metamaterial show the sample sensitivity to different symmetries of the electric field distributions, as well as the important role of the longitudinal field components of the beam on the extinction. Strong dichroism of the anisotropic metamaterial results in variations of the beam modal structure by differently influencing the three components of the field. Moreover, decomposing the beam intensity profiles in the Laguerre-Gauss mode basis reveals a non-negligible variation of the modal content of the beam, induced by the nanorod metamaterial anisotropy. Linear, radial and azimuthal polarisation states have been tested for metamaterials with different anisotropy parameters. Experimental results show a good agreement with the theoretical predictions, proving the promising potential of anisotropic metamaterials for manipulation of complex vector beams.
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