Controlling the propagation and coupling of light to sub-wavelength antennas is a crucial prerequisite for many nanoscale optical devices. Recently, the main focus of attention has been directed towards high-refractive-index materials such as silicon as an integral part of the antenna design. This development is motivated by the rich spectral properties of individual high-refractive-index nanoparticles. Here, we take advantage of the interference of their magnetic and electric resonances, to achieve remarkably strong lateral directionality. For controlled excitation of a spherical silicon nanoantenna we use tightly focused radially polarized light. The resultant directional emission depends on the antennas position relative to the focus. This approach finds application as a novel position sensing technique, which might be implemented in modern nanometrology and super-resolution microscopy setups. We demonstrate in a proof-of-concept experiment, that a lateral resolution in the Angstrom regime can be achieved.
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