Transient optical symmetry breaking for ultrafast broadband dichroism in plasmonic metasurfaces

TL;DR

This paper demonstrates that ultrafast, reversible symmetry breaking in plasmonic metasurfaces induces broadband transient dichroism, enabling picosecond-scale polarization modulation for ultrafast nanophotonic devices.

Contribution

It introduces a novel mechanism of transient symmetry breaking caused by hot carrier inhomogeneities, leading to ultrafast broadband dichroic responses in plasmonic metasurfaces.

Findings

Transient symmetry breaking induces broadband dichroism.

Reversible process with sub-1 ps recovery.

Potential for Tera bit/s light polarization modulation.

Abstract

Ultrafast nanophotonics is an emerging research field aimed at the development of nanodevices capable of light modulation with unprecedented speed. A promising approach exploits the optical nonlinearity of nanostructured materials (either metallic or dielectric) to modulate their effective permittivity via interaction with intense ultrashort laser pulses. While the ultrafast temporal dynamics of such nanostructures following photoexcitation has been studied in depth, sub-ps transient spatial inhomogeneities taking place at the nanoscale have been so far almost ignored. Here we theoretically predict and experimentally demonstrate that the inhomogeneous space-time distribution of photogenerated hot carriers induces a transient symmetry breaking in a plasmonic metasurface made of highly symmetric metaatoms. The process is fully reversible, and results in a broadband transient dichroic optical response with a recovery of the initial isotropic state in less than 1 picosecond, overcoming the speed bottleneck caused by slower relaxation processes, such as electron-phonon and phonon-phonon scattering. Our results pave the way to the development of ultrafast dichroic devices, capable of Tera bit/s modulation of light polarization.