Ultrafast all-optical metasurfaces: controlling light and manipulating matter

Achieving fast and active temporal control of optical metasurfaces remains an open challenge in nanophotonics. Such control would dramatically enhance the scopes of metasurfaces, as their functionalities could be tuned on demand, beyond the limits of their static properties. Here we report on our approach to design and demonstrate the control of all-optically tunable metasurfaces in the ultrafast regime in different scenarios. First, we theoretically predict and experimentally prove by ultrafast transient absorption spectroscopy that spatio-temporal dynamics of hot electrons can promote and control a sub-picosecond photoinduced anisotropy in plasmonic metasurfaces, enabling active reconfiguration of the nanostructure nonlinear response. Then, we demonstrate a giant all-optical modulation of dichroism in an anisotropic all-dielectric metasurface. Finally, we propose a new paradigm exploiting the unique properties of active ultrafast metasurfaces for controlling physico-chemical processes activated by light to improve their efficiency.