Radiative coupling of high-order plasmonic modes with far-field

In the last few years, hybrid systems consisting of punctual sources and metallic nanostructures have been assembled and studied. Furthermore, the radiative coupling between the two counterparts has become a crucial aspect to be explored in nanophotonics and plasmonics. In this paper a numerical framework based on the Discrete Dipole Approximation is presented as a simple computational scheme to analyze the decay dynamics of an emitter when it is located in the near proximities of metallic nanoparticles. This approach allows to go beyond the analytically solved cases and to predict the optical response of more complex shaped nanoparticles. Here the excitation of dipole and higher-order modes is studied as a function of the applied radiation with a particular attention paid to the changes induced in the response by approaching the source to the metal. Numerical results, obtained for Ag spheroids and conically shaped nanoparticles, are explained by analyzing the charge density induced on the surface of the nanoparticles, this allowing to distinguish dark from radiative modes in a straightforward way.