All‐Optical Reconfiguration of Ultrafast Dichroism in Gold Metasurfaces

Abstract

Optical metasurfaces have come into the spotlight as a promising platform for light manipulation at the nanoscale, including ultrafast all‐optical control via excitation with femtosecond laser pulses. Recently, dichroic metasurfaces have been exploited to modulate the polarization state of light with unprecedented speed. This work theoretically predicts and experimentally demonstrates by pump–probe spectroscopy the capability to reconfigure the ultrafast dichroic signal of a gold metasurface by simply acting on the polarization of the pump pulse, which is shown to reshape the spatio‐temporal distribution of the optical perturbation. The photoinduced anisotropic response, driven by out‐of‐equilibrium carriers and extinguished in a sub‐picosecond temporal window, is readily controlled in intensity by tuning the polarization direction of the excitation up to a full sign reversal. Hence, nonlinear metasurfaces are here demonstrated to offer the flexibility to tailor their ultrafast optical response in a fully all‐optically reconfigurable platform.

Ultrafast All-Optical Metasurfaces: Challenges and New Frontiers

“…The hot-carrier pattern can be shaped by rotation of the pump polarization, offering a way to change the output polarization with the exciting pulse, up to a sign reversal of the transient dichroism. 127 While more sophisticated approaches can speed up the modulation of plasmonic all-optical platforms, none of them enables to reduce the intrinsic, large absorption losses of metals. Switching to alternative material platforms is mandatory for this challenge, which can be addressed with high-index semiconductors, representing excellent candidates to develop more power-efficient architectures.…”

Plasmon-induced hot carrier dynamics and utilization

“…For instance, Schirato et al reported an all-optical reconfiguration of ultrafast dichroism in Au metasurfaces consisting of two-dimensional Au symmetric nanocross structures [Fig. 20(a)] [377] . The metasurface has a fourth-fold symmetry, so its light absorption properties are invariant with the light polarization.…”

“…(a) Transient linear dichroism of a metasurface consisting of a lattice of Au symmetric nanocrosses. The first femtosecond pump pulse breaks the fourfold symmetry by generating hot carriers, and then a second femtosecond probe pulse with a time delay of 100 fs shows the dichroism dependent on the polarization of the pump pulse [377] . (b) Ultrafast all-optical control of the polarization of light by Au array/ITO/Au film/silicon substrate.…”