Influence of the tip in near-field imaging of nanoparticle plasmonic modes: Weak and strong coupling regimes

We identify weak and strong coupling regimes between a near-field probing tip and a plasmonic sample by imaging plasmon-resonant gold nanodisks with scattering-type scanning near-field optical microscopy (s-SNOM). By means of rigorous electrodynamical calculations based on a model system, we find that in the weak coupling regime, s-SNOM can be applied for direct mapping of plasmonic nanoantenna modes, while in the strong coupling regime, the near-field probe allows for high-precision opto-mechanical control of the antenna response.