Ultrafast Electron Dynamics and Optical Nonlinearities in Metal Nanoparticles

Abstract

The femtosecond optical response of noble metal nanoparticles and its connection to the ultrafast electron dynamics are discussed in light of the results of high-sensitivity femtosecond pump-probe experiments. The physical origins of the nonlinear responses in the vicinity of the surface plasmon resonance and interband transition threshold are analyzed using extension of the theoretical models used in the bulk materials. These responses contain information on the electron interaction processes (electron-electron and electron-phonon scattering) that can thus be directly investigated in the time domain. Their size and environment dependences are discussed, and the results are compared to the ones in the bulk materials. Time-resolved techniques also permit direct study of the vibrational modes of metal nanoparticles and, in particular, the determination of their damping, which is a sensitive probe of the nature of the surrounding matrix and of the interface quality.

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…This is attributed to a direct launching mechanism previously observed in solid Au nanoparticles, which also have sinusoidal frequencies, and is believed to be the result of deformation caused by the incident laser pulse [132,154]. High aspect ratio HGNs had a phase shift and required a cosine function to fit the data indicative of excitation via an indirect mechanism [132,153]. It was also determined that high aspect ratio HGNs have slower vibrations than low aspect ratio HGNs due to polycrystallinity of the shell lattice and efficient cooling processes and that there is an inversely proportional linear relationship between vibrational frequency and aspect ratio [155].…”

“…Faster electronic relaxation is attributed to greater electron-phonon coupling [141]. The transfer of energy between hot electrons and the nanoparticles can be observed as coherent vibrational oscillations which are indicative of the breathing modes of the nanoparticle lattice [57,152,153]. The amplitude of the coherent oscillations of HGNs can be correlated to aspect ratio since amplitude is inversely proportional to the electron-phonon coupling constant g [153,154].…”

“…The transfer of energy between hot electrons and the nanoparticles can be observed as coherent vibrational oscillations which are indicative of the breathing modes of the nanoparticle lattice [57,152,153]. The amplitude of the coherent oscillations of HGNs can be correlated to aspect ratio since amplitude is inversely proportional to the electron-phonon coupling constant g [153,154]. When Dowgiallo et al investigated HGNs with aspect ratios of 0.38 and 0.75 using femtosecond laser spectroscopy it was found that the lower aspect HGNs had a modulated signal intensity that was only 65% of the amplitude observed for the higher aspect ratio HGNs [155].…”

Gold nanoparticle assemblies: interplay between thermal effects and optical response

“…Here, we present the main different approaches and the most recent developments, before applying them in the last section to the determination of the role of some thermal effects in the nonlinear optical response of nanocomposites. 6263646566676869707172 The response of a nanocomposite medium to a laser pulse is ruled by a series of different mechanisms, each exhibiting its own dynamics [62][63][64][65][66][67][68][69][70][71][72]: light energy absorption by electrons, redistribution within the conduction electron gas through electron-electron collisions, relaxation toward metal lattice by electron-phonon scattering, and then particle cooling down by heat transfer to the surrounding medium. Note that the short time domain of the relaxation -the first few picoseconds after excitation -has been widely investigated by several groups [62,65,68,70].…”

Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire

“…In this approach, a first blue pump pulse excites the conduction electrons of the metallic nano-object. The subsequent electron cooling by electron-lattice interactions [30] results in the heating of the crystal lattice finally launching the dilatation of the nanowire [31,32]. Because of the electrons fast diffusion, this ultrafast heating is not confined to the surface of the nano-object, the whole width of the nanowire subsequently undergoes periodic radial contrac- tions and expansions.…”