Transient Optical Response of a Single Gold Nanoantenna: The Role of Plasmon Detuning

Abstract

We study by femtosecond pump-probe microscopy the transient plasmonic response of individual gold nanoantennas fabricated by electron-beam lithography on a glass substrate. By exploiting the capability of the fabrication technique to control geometrical parameters at the nanoscale, we tuned the plasmonic resonance in a broad wavelength range, from the visible to the infrared. Numerical simulations based on a three-temperature model (3TM) for the electrons and lattice dynamics, combined with * To whom correspondence should be addressed full-wave numerical analysis and semiclassical theory of optical transitions in the solid state, are compared with the measurements on a single gold nanoantenna probed at different wavelengths. The agreement between the experiment and the prediction of the 3TM turns out to be comparable to that achievable with the more sophisticated Boltzmann equation formalism. We also investigate the influence of the plasmon detuning with respect to the pump and probe wavelengths on the nonlinear optical response using different nanoantennas. Quantitative comparison of the experimental data with the theoretical model also provides a disentanglement of the different contributions to the optical nonlinearity of gold giving rise to the complex features observed in the transient optical response. Our study provides a complete analysis of the physical mechanisms dominating the nonlinear plasmon dynamics of an individual nanoobject taking place on a few ps time scale.

Light–heat conversion dynamics in highly diversified water-dispersed hydrophobic nanocrystal assemblies

“…The pump absorption initiates a chain of energy transfer processes. In the spirit of the semiclassical models reported for plasmonic nanomaterials [noble metals (33) and heavily doped (34) and even alldielectric (35) semiconductors] a set of dynamical variables (usually temperatures) describing the different energy degrees of freedom is introduced and coupled together in a system of rate equations. For the hybrid metal-organic structure of Au assemblies we adopted the following four-temperature model (4TM):Ṅ = pa (t) − aN ,…”

“…Note that Eqs. 1-3 basically represent the three-temperature model (3TM) which successfully describes the relaxation dynamics of Au NCs, being γ = 68 J·m −3 ·K −2 the electrons' heat capacity constant, cL = 2.5 × 10 6 J·m −3 ·K −1 the lattice heat capacity of gold, g = 2.2 × 10 16 W·m −3 ·K −1 the electron-phonon coupling constant, and a = 15 THz the hot electrons' heating rate at 400-nm pumping (33). The 3TM of gold is then coupled to a fourth equation, Eq.…”

“…The corresponding ∆ N , ∆ E , and ∆ L, are retrieved by following the same approach detailed in previous papers on the 3TM of gold (e.g., ref. 33 and references therein). Regarding the permittivity variation induced in the organic matrix, this is computed as ∆ O = 2nO η∆ΘO , with η = dnO /d ΘO being a negative thermo-optics coefficient, of the order of −10 −4 K −1 (37) (to be fitted on the experimental data), and ∆ΘO being the increase of the matrix temperature.…”

Anomalous ultrafast dynamics of hot plasmonic electrons in nanostructures with hot spots

“…After excitation, plasmons are absorbed by the metal electrons through inter-and intraband transitions, creating a highly non-thermal distribution of electrons [2][3][4] . The electron population then decays through electron-electron interactions, creating a hot electron distribution within a few hundred femtoseconds, followed by a further relaxation via electron-phonon scattering on the timescale of a few picoseconds [5][6][7][8] . In the spectral domain, hot plasmonic electrons induce changes to the plasmonic resonance of the nanostructure by modifying the dielectric constant of the metal 5,9 . Here, we report on the observation of anomalously strong changes to the ultrafast temporal and spectral responses of these excited hot plasmonic electrons in hybrid metal/oxide nanostructures as a result of varying the geometry and composition of the nanostructure and the excitation wavelength.…”

Experimental and Ab Initio Ultrafast Carrier Dynamics in Plasmonic Nanoparticles

“…DOI: 10.1103/PhysRevLett.118.087401 Plasmonic hot carriers provide tremendous opportunities for combining efficient light capture with energy conversion [1][2][3][4][5] and catalysis [6,7] at the nanoscale [8][9][10]. The microscopic mechanisms in plasmon decays across various energy, length, and time scales are still a subject of considerable debate, as seen in recent experimental [11,12] and theoretical literature [13][14][15][16]. The decay of surface plasmons generates hot carriers through several mechanisms, including direct interband transitions, phonon-assisted intraband transitions, and geometry-assisted intraband transitions, as we have shown in previous work [17,18].…”