Nonlinear modes in time-modulated structures

In time-varying plasmonic structures, novel electromagnetic phenomena arise from the combined manipulation of spatial and temporal degrees of freedom. These systems have recently attracted significant scientific interest due to their potential applications in time-varying metamaterials, metasurfaces, nonreciprocal devices, and parametrically resonant systems. This work investigates space-time-varying plasmonic structures that leverage the second-order and third-order nonlinearity of their constituent materials to modulate permittivity. When a pump field modulates material properties at a frequency close to that of a probe field, the phase relationship between the pump and probe becomes crucial, leading to what we term “coherent plasmonic structures.” By harnessing wave-mixing interactions in time-modulated plasmonic scatterers, we demonstrate the selective nonlinear excitation of system modes. Our analysis shows that intermodal energy transfer enables the excitation of high-order resonances from zero initial amplitude.