We design and fabricate a metasurface composed of gold cut-disk
resonators that exhibits a strong coherent nonlinear response. We experimentally
demonstrate all-optical modulation of both second- and third-harmonic signals on a
subpicosecond time scale. Pump−probe experiments and numerical models show
that the observed effects are due to the ultrafast response of the electronic
excitations in the metal under external illumination. These effects pave the way for
the development of novel active nonlinear metasurfaces with controllable and
switchable coherent nonlinear response
