Simple and robust analytical model for dipolar resonances in plasmonic particle-substrate systems

We revisit the theory of light-matter interactions induced by a small metallic particle near a planar surface. The resonant features of the coupled system are investigated using an approach that determines the particle permittivity that brings the system to resonance. Analytical results are presented for the case of a spherical particle near a flat substrate and compared to previous results, whereas a general recipe involving Green's function is also given. In contrast to previous work, our analytical results allow the determination of eigenfrequencies in the presence of strong temporal dispersion and include radiative damping. Furthermore, the model can be related to stationary normal modes, thereby providing physical insight and a design tool for surface-enhanced devices and sensing.