Design of symmetric nanoresonators to scale the ultrafast optical modulation in plasmonic metasurfaces

The light-driven control over the properties of optical nanostructured materials has been shown to be a promising route to achieve various functionalities, possibly on sub-picosecond time scales when ultrashort pulses are employed. Here, we discuss how to induce and reveal an ultrafast dichroism in a set of plasmonic metasurfaces with increasing symmetry by using femtosecond pump-probe spectroscopy. We show that such effect is general, promoted by the photogeneration of out-of-equilibrium electrons, and it can be induced in any sufficiently large nanoresonator, provided that plasmonic modes with well-defined symmetry are excited. The intensity of the photoinduced ultrafast dichroisms depends on the geometry of the nanoresonator, and scales up when the excitation symmetry of the plasmonic mode decreases. Our comparative analysis demonstrates the possibility to exploit light-matter interaction as an effective tool to manipulate transient optical symmetry of metasurfaces.