Geometry Defines Ultrafast Hot‐Carrier Dynamics and Kerr Nonlinearity in Plasmonic Metamaterial Waveguides and Cavities

Hot carrier dynamics in plasmonic nanorod metamaterials and its influence on the metamaterial's optical Kerr nonlinearity is studied. The electron temperature distribution induced by an optical pump in the metallic component of the plasmonic metamaterial leads to geometry‐dependent variations of the optical response and its dynamics as observed in both the transmission and reflection properties of the metamaterial slab. Thus, the ultrafast dynamics of a metamaterial's optical response can be controlled via modal engineering. Both the transient response relaxation time and magnitude of the nonlinearity are shown to depend on the modal‐induced spatial profile of the electron temperature distribution and the hot‐electron diffusion in nanorods. The nonlocal effects, depending on the excitation‐induced losses in the metal, are shown to dictate the modal structure of the metamaterial slab and the associated dynamics of its nonlinear response. The opportunity of controlling the electron temperature profile induced in the plasmonic nanorods by changing the metamaterial's geometry and/or excitation conditions paves the way to achieve controllable dynamics of the nonlinear optical response for free‐space as well as integrated nanophotonic applications involving nonequilibrium electrons.