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Focusing surface plasmons on Er3+ ions with convex/concave plasmonic lenses

Plasmonic lenses consisting of convex/concave concentric rings with different periods were milled with a Focused Gallium Ion Beam on a gold thin film deposited onto an Er3+-doped tellurite glass. The plasmonic lenses were vertically illuminated with an Argon Ion laser (488 nm) highly focused by means of a 20x objective lens. The focusing mechanism of the plasmonic lenses is explained by using a simple coherent interference model of surface plasmon-polariton generation on the circular grating as a result of the incident field. Particularly, this beam focusing structure has a modulated groove depth (concave/convex). As a result, phase modulation can be accomplished by the groove depth profile, similarly to a nano-slit array with different thicknesses. This focusing allows a high confinement of SPPs which excited the Er3+ ions of the substrate. The luminescence spectrum of Er3+ ions was then measured in the far-field, where we could verify the excitation yield of the plasmonic lens on the Er3+ ions. We analyze the influence of physical and geometrical parameters on the emission spectra, such as the periodicity and depth profile of the rings. The variation of these parameters resulted in considerable changes of the luminescence spectra.