Quantifying single plasmonic nanostructure far -fields with interferometric and polarimetric k-space microscopy

Optically resonant nanoantennae are key building blocks for metasurfaces, nanosensors and nanophotonic light sources due to their ability to control the amplitude, phase,
directivity and polarization of scattered light. Here, we report an experimental technique
for the full recovery of all degrees of freedom encoded in the far-field radiated by a
single nanostructure using a high-NA Fourier microscope equipped with digital off-axis
holography. This method enables full decomposition of antenna-physics in its multipole
contributions and gives full access to the orbital and spin angular momentum properties
of light scattered by single nano-objects. Our results demonstrate these capabilities through a quantitative assessment of the purity of the ‘selection rules’ for orbital angular momentum transfer by plasmonic spiral nanostructures.