Light-matter interactions at the nanoscale: Harmonic generation from metal/vacuum interfaces and radiation reaction

I will first briefly describe a microscopic Maxwell-hydrodynamic model that can be used to explore a range of linear and nonlinear optical phenomena at the nanoscale, ranging from harmonic generation from metal/vacuum interfaces to Silicon-based metasurfaces, and combinations of plasmonic and epsilon-near-zero resonances to high harmonic generation from coupled Bloch equations that describe multilevel systems beyond the rotating and slowly varying envelope approximations. I will then focus on harmonic generation from metal/vacuum interfaces and novel aspects of the theory of damping that can affect optics at the nanoscale. More specific to noble metals, a patina of free electrons extends out into free space and vanishes within an atomic diameter. We discuss the possibility and consequences of such a free electron layer acting as an epsilon-near-zero layer and how this “equivalent material” can enhance the local field and nonlinear conversion efficiencies by several orders of magnitude.