Angle-Resolved Polarimetry of Bullseye Plasmon Antennas

An ultimate goal of nanophotonics is to engineer single nanostructures, or clusters of them, capable of precisely manipulating the propagation, emission and absorption of light. Here we introduce angle-resolved polarimetry as a technique to measure the response of single scatterers to different excitations and incident fields. This technique combines a device capable of mapping the k-vector distribution of scattered radiation (i.e. a Fourier microscope or an angle-resolved cathodoluminescence system) with a polarimeter that measures the full polarization state for each wave vector. For a given incident k-vector distribution, an angle-resolved polarimeter measures all information encoded in the transmission function of a scatterer up to an over-all phase.

To demonstrate angle-resolved polarimetry we consider bullseye antenna scatterers, consisting of periodic grooves concentric to a circular hole in a plasmonic metal film. These antennas are among the simplest, most widely used, and best understood plasmonic structures that scatter light directionally. Bullseye antennas are also widely studied for their ability to impart directionality to fluorescence.

We studied the behavior of bullseye antennas either illuminated by linearly or circularly polarized light or excited by the focused electron beam of an electron microscope. In the first case, we measured the angle-resolved polarization state of light scattered by the structure and of the fluorescence of fluorophores residing in its central aperture. In the second case, we determined the full polarization state of the cathodoluminescence emission of bullseye antennas as a function of the emission angle.

Our results not only evidence some remarkable features of the scattering of bullseye antennas, for instance strong linear-to-circular polarization conversion at off-normal scattered wave vectors, but also the potential of the reported technique to test our understanding of a plethora of dielectric and metallic nanophotonic structures.

c.osorio@amolf.nl