Probing spin-orbit interaction via Fano interference

We experimentally investigate the behavior of the Fano-like plasmonic resonance lineshape in a simple plasmonic system comprising a subwavelength hole or a particle illuminated by a tightly focused Gaussian beam. We observe that for a small lateral displacement of the scatterer, the k-space distribution of the plasmonic wave exhibits a strong spin-dependent azimuthal variation. We attribute this phenomenon to the sensitive light-plasmon coupling conditions arising due to the specific phase matching requirements. This effect is qualitatively described by a Fano-like interference with a complex coupling factor.