Lorentz-Drude dipoles in the radiative limit and their modeling in finite-difference time-domain methods

The Lorentz-Drude model for electric dipoles is a classical framework widely used in the study of dipole dynamics and light-matter interactions. Here we focus on the behaviors of Lorentz-Drude dipoles when their radiative rate dominates their energy loss. We show that dipole radiation losses do not count toward phenomenological dipole losses if the driving field is interpreted as the total field at the dipole. In particular, if the dipole does not contain non-radiative losses, then the Lorentz-Drude damping term should be removed. This is verified by self-consistent implementations of point dipoles in finite-difference time-domain simulations, which also provide a method to directly compute the transport properties of light when dipoles are present.