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Soutenance de thèse - Xiaoli Wang

Equipe « Acoustique pour les nanosciences » de l’INSP

19 juin 2013 à 14h - Amphi Chemla, Institut d’Alembert - Ecole Normale Supérieure de Cachan

« Photo-induced ultrafast optical and thermal responses of gold nanoparticles »

Abstract

Gold nanoparticles (NPs) under light irradiation exhibit collective oscillations of their conduction electrons, known as the localized Surface Plasmon Resonance (SPR). The SPR then enables efficient and quick energy input in NPs through absorption of ultrafast laser pulses. A series of energy conversion and exchange mechanisms follows involving electron‐electron and electronphonon scattering. The subsequent NP heating further relaxes by thermal transfer to the host medium. Gold NPs under light pulses can thus be used as local ultrafast heat nanosources. Furthermore, the different photo‐induced processes result in the transient modification of the NP optical properties, which can be monitored by time‐resolved pump‐probe laser spectroscopy. The energy input and optical response, as being mainly linked with the SPR, are very sensitive to the NP morphological parameters like size, shape and spatial distribution in the host medium.

In this work, we study and exploit several aspects of the ultrafast transient optical response of gold NPs. We first review the theoretical fundamentals and models, as well as the experimental technique that we have carried out. Then the spectral dependence of the optical response of gold nanorods is investigated. Further, we analyze also the effect of plasmon coupling on the stationary and transient optical properties of gold NP arrays. Moreover, we investigate and exploit the ultrafast transient resonant coupling of the SPR of gold NPs and a localized cavity mode in a 1D photonic crystal. Finally, we study the local photo‐induced heating properties of several kinds of NPs.