Nonperturbative Hydrodynamic Model for Multiple Harmonics Generation in Metallic Nanostructures

The electromagnetic response of a free-electron gas leads to the inherent nonlinear optical behavior of nanostructured plasmonic materials enabled through both strong local field enhancements and complex collective electron dynamics. Here, a time-domain implementation of the hydrodynamic model for conduction electrons in metals has been developed to enable nonperturbative studies of nonlinear coherenet interactions between light and plasmonic nanostructures. The effects originating from the convective acceleration, the magnetic contribution of the Lorenz force, the quantum electron pressure, and the presence of the nanostructure's boundaries have been taken into account, leading to the appearance of both second and third harmonics. The proposed time-domain method enables obtaining a universal, self-consistent numerical solution, free from any approximations, allowing investigations of nonlinear optical interactions with arbitrary spatially and temporally shaped optical pulses, opening unique opportunities to approach description of realistic experimental scenarios.