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Here I investigate both numerically and experimentally, the polarization conversion capabilities of a rectangular array of holes with two unequal orthogonal periodicities. We show that it is possible to tune the periodicities in such a way that the transmitted light is circularly polarized for a nominated wavelength, Lambda-CPL, when the structure is illuminated with appropriately oriented linearly polarized light at normal incidence. A device was fabricated and experiments confirmed that a degree of circular polarization of 0.89 could be achieved at the resonant wavelength., Comment: Some historical facts added to the end

Progress in the excitation of ‘dark-modes’ in plasmonic structures is reported. The interaction of vector beams possessing a spatially inhomogeneous polarization profile with plasmonic nanostructures provides an avenue to probe these resonances.

Plasmonic dark modes are pure near-field modes that can arise from the plasmon hybridization in a set of interacting nanoparticles. When compared to bright modes, dark modes have longer lifetimes due to their lack of a net dipole moment, making them attractive for a number of applications. We demonstrate the excitation and optical detection of a collective dark plasmonic mode from individual plasmonic trimers. The trimers consist of triangular arrangements of gold nanorods, and due to this symmetry, the lowest-energy dark plasmonic mode can interact with radially polarized light. The experimental data presented confirm the excitation of this mode, and its assignment is supported with an electrostatic approximation wherein these dark modes are described in terms of plasmon hybridization. The strong confinement of energy in these modes and their associated near fields hold great promise for achieving strong coupling to single photon emitters.