Towards complete optical coupling to confined surface polaritons

We demonstrate a novel method for effectively coupling light with surface-plasmon polaritons using specially designed dipolar scatterers strategically positioned at an optimal distance from the surface. In our experiments, we constructed gold disks with a silica spacer from a flat gold surface and adjusted the spacer thickness to match a specific scatterer geometry that resonates at a predetermined optical frequency. This setup achieved a peak coupling efficiency of light to plasmon that is comparable to the square of the light's wavelength, at an ideal distance facilitated by the balance between strong particle-surface interactions and minimal surface-induced particle-dipole damping, both of which are enhanced at closer distances. Our findings, which are consistent with both analytical theory and electromagnetic simulations, propose the use of strategically placed scatterers as an innovative solution to the longstanding issue of efficient coupling in and out of nanophotonic systems.