Structured light beams with space-variant polarization can be efficiently generated using a voltage-tunable nematic liquid crystal ($Q$ plate). By appropriately selecting the input state and the retardation of the $Q$ plate, an optical field acquires a spatially structured polarization distribution that is capable of encoding nontrivial topological information across the beam profile. These features can be directly read out through interaction with plasmonic nanostructures, such as circular and spiral slits. Here we show that, upon illumination, polarization-dependent excitation of surface plasmons converts the hidden topology of the polarization structure into observable intensity distributions, including plasmonic vortices and characteristic interference patterns, while the tunability of the input parameters enables a rich variety of distinct topological forms.

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• Angular momentum of light
• Beam optics
• Beam polarization
• Plasmons
• Structured light