Ultrafast Resonant Dynamics of Surface Plasmons in Gold Nanorods

Abstract

Electron dynamics in Au nanorods are studied with femtosecond nonlinear spectroscopic techniques, by directly exciting and probing the longitudinal surface plasmon resonance. The dispersive and absorptive parts of the third-order signal are measured using optical heterodyne detected four-wave-mixing spectroscopy. These signals are used to describe dynamics in Au nanorods in terms of frequency shift and broadening of the plasmon resonance. Pump−probe experiments are performed with a series of pump intensities. The results are treated in two ways: (1) by calculating the temperature changes of electrons and phonons in the nanorods and the effects of these temperatures on the dielectric constant of Au; and (2) by a nonlinear least-squares fitting using a phenomenological response function. The first model agrees with the pump−probe experimental results for pump energies up to 2.0 nJ (2.5 GW/cm2) and for delays in the range of 150 fs to 150 ps, but does not reproduce three additional features present in the data and the phenomenological model: (1) an “instantaneous” response, attributed to coherent plasmon oscillation; (2) a decaying component with an intensity-independent time constant of 170 fs, attributed to a nonthermal electron distribution or to two-photon-excited interband transitions; and (3) oscillations with a period of 71 ps, attributed to coherent vibration of the rods. Higher pump intensities yield substantial deviation at short delays from the lower-intensity response. Additional plasmon damping and higher-order nonlinear mechanisms are suggested to account for these deviations.

Metal‐nanoparticle plasmonics

“…Although the measurements can reveal information about electron dynamics in the particles, they cannot directly probe the nonlinear response of the plasmon resonances. This, by contrast, requires a wavelength-degenerate measurement, so that the pump and probe are both resonant with the plasmons [111]. This was recently attempted using gold nanorods similar to those in Fig.…”

Silicon-Based Plasmonics for On-Chip Photonics

“…In addition, the reduced surface plasmon wavelength can enable high quality factor microcavities [54] that confine light well below the diffraction limit. Combined, these plasmonic effects have enabled novel devices for on-chip nonlinear optics [44], [64], quantum optics [21], and lasing [35].…”

Probing the acoustic vibrations of single metal nanoparticles by ultrashort laser pulses

“…The period of the vibrations displayed a linear increase with particle size, and the extracted sound velocities were found to be consistent with those of the bulk material. Subsequently, coherently excited acoustic vibrations in metal nanoparticles were studied in ensembles of spheres [23,36,37,[54][55][56][57], rods [23,[58][59][60][61][62], core-shell spherical particles [63], ellipsoids [28], disks [64], cubes [65], boxes and cages [66], triangles [67], columns [68] and bipyramids [69]. These investigations yielded valuable information on the frequency of the fundamental breathing vibration modes of these particles, from which in some cases the elastic constants of the particles could be extracted [61,70].…”