Polarization-resolved femtosecond pump-probe spectroscopy for Au nanodisks at the LSP resonance

Abstract

The formation and relaxation of plasmon-induced hot electrons in Au nanodisks (AuNDs) with relatively large particle size was studied by femtosecond pump-probe spectroscopy. We temporally resolved the plasmon-induced formation of nonthermal electrons through intraband transitions and subsequent redistribution of nonthermal electrons to thermal electrons. The transient extinction spectra were found to exhibit clear dichroism for the pump polarization on a time scale of a few hundred femtoseconds. The electric field distribution was calculated using the Finite-difference time-domain (FDTD) method to be inhomogeneous inside the AuNDs under irradiation by linearly polarized light. The formation and relaxation of hot electrons occur locally inside the AuNDs, which results in the observed ultrafast dichroic response.

All‐Optical Reconfiguration of Ultrafast Dichroism in Gold Metasurfaces

“…Note that such a light-enabled control of the optical symmetry is not restricted to fourfold symmetric cross-shaped nanostructures, and has more general validity. A transient photoinduced anisotropy has been recently reported for metasurfaces with different unit-cell geometries sharing with the nanocrosses presented here (and in previous reports [35] ) the C4 symmetry (plates [43] ), or exhibiting even higher symmetry (disks [36,43] ) in unperturbed conditions.…”

“…dichroism. [35,36] However, the possibility to reconfigure this dichroism, dictated by the anisotropy (either geometrical or optical) of the structure, has not been explored so far, unless on extremely long time scales. [37,38] In this work, we theoretically predict and experimentally demonstrate all-optical reconfiguration of the ultrafast linear dichroism photogenerated in a nonlinear plasmonic metasurface consisting of symmetric gold cross-shaped meta-atoms.…”

“…In this framework, the schemes considered so far involved structures exhibiting either an intrinsic non‐zero dichroic response, [ 30–34 ] or a transient photoinduced linear dichroism. [ 35,36 ] However, the possibility to reconfigure this dichroism, dictated by the anisotropy (either geometrical or optical) of the structure, has not been explored so far, unless on extremely long time scales. [ 37,38 ]…”

Hot carrier spatio-temporal inhomogeneities in ultrafast nanophotonics

“…To the best of our knowledge, only a limited number of recent works have focused, either theoretically [45][46][47][48][49] or with experimental evidence as well [50][51][52][53][54][55], on the role of hot-carrier nanoscale spatial inhomogeneities in ultrafast nanophotonics. In particular, it has been shown that hot carrier diffusion, typically requiring hundreds of femtoseconds to lead to homogenization of the excitation, may play a major role in sub-ps light manipulation schemes.…”