Transient localized surface plasmon induced by femtosecond interband excitation in gold nanoparticles

Abstract

Localized surface plasmon resonance (LSPR) is essentially a collective oscillation of free electrons in nanostructured metals. Interband excitation may also produce conduction-band electrons above the Fermi level. However, a question here is whether these excited electrons can take part in plasmonic oscillation. To answer this question, femtosecond pump-probe measurements on gold nanoparticles were performed using interband excitation, where the pump pulse produced a large amount of electrons in the sp-conduction band and left holes in the d-band. Probing by transient absorption spectroscopy, we resolved an induced LSPR feature located at a red-shifted spectrum. This feature cannot be observed for a pumping photon energy lower than the threshold for interband transition. The commonly observed red-shift or broadening of LSPR spectrum due to electron-electron and electron-phonon scattering under strong optical excitation can be ruled out for understanding this feature by a comparison between the plasmonic dynamics at a pump above and below the interband-transition threshold. In particular, a “holding” time of about 1 ps was resolved for the interband-excitation-induced electrons to relax to the LSPR oscillation.

In situstructural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres

“…37,61 Additionally, it has been reported that excitation at (or close to) the plasmon resonance (here 532 nm) is less efficient due to delocalized field distribution 65,66 or ultrafast plasmon band bleaching. 67 Indicative of the latter is also the observation the bubble formation threshold in the current experiment is found at about 56 J m À2 , which is not much lower than the previously recorded threshold of 80 J m À2 at 400 nm (femtosecond pulses) 61 or 50 J m À2 at 355 nm (picosecond pulses) 68 for similarly sized gold particles, despite the absorption cross section being enhanced by a factor of 2 at 532 nm. Altogether, we can secure the general caloric scale for the excitation of the gold nanoparticle suspension, noting that melting is observed above 120 J m À2 .…”

Ultrafast Investigation of Individual Bright Exciton–Plasmon Polaritons in Size‐Tunable Metal–WS2 Hybrid Nanostructures

“…This blue‐shift is assigned to the cooling of hot electron population of AuNI via both elastic and inelastic electron scattering processes that typically occur in sub‐picosecond timescales. [ 41–43 ] Now, as the individual spectral positions of both the bright excitons (X 0 A and X 0 B ) are already known in WS 2 , the Rabi‐splitting energy can be calculated by directly solving E + and E − . The extracted individual Rabi‐splitting energies (Ω R ) are found to be 269 ± 26 and 246 ± 7 meV for X 0 A ‐P and X 0 B ‐P, respectively, in the time domain, by fitting the transient peak positions of E + and E − with Equation ().…”

Quantitative Ultrafast Electron‐Temperature Dynamics in Photo‐Excited Au Nanoparticles

“…as well as the constituent material, the size and shape of the NPs, can all play a crucial role in the e-gas heating and in the energy-relaxation pathway. [23][24][25][26][27][28][29][30][31][32] Additionally, the temperature dependence of the material paratemers (e.g., electronic specific heat, [33][34][35] interface thermal conductivities, [36] etc.) will all affect the actual relaxation dynamics.…”