Ultrafast Dynamics of Metallo-Dielectric Core-Shell Particles

Abstract

Optical properties of metallic nano-structures have attracted a lot of attention in the past decades. In this thesis, we focus on nano-sized silica-core gold-shell particles, study the linear, nonlinear and acoustic vibrations of the particles. The linear optical properties in the visible range of gold-shell particles are analyzed both in ordered and disordered arrays, in reflection and transmission. A transmission window was observed from 500 nm to 650 nm, which is interpreted as plasmon conduction in the photonic stop band. Highly directional diffraction patterns, with hexagonal or cubic symmetry, were observed in the photonic crystal structure, corresponding to Fraunhofer diffraction of a collection of well organized small crystallites. The ultrafast electronic response of a 3-D gold-shell photonic crystal of these particles following femtosecond optical excitation is analyzed by ultrafast pump-probe experiments, which can be described by the so-called two-temperature model. Acoustic vibrations were observed following the ultrafast response. In spherical particles, the vibrational period depends on the gold-shell size and can be calculated by a two-shell model developed on basis of Lamb theory. On elliptical particles, the acoustic vibrational periods generated, show a dependence on the orientation of particles, and correspond to the longitudinal vibrations along the long and short axes, respectively.