Improved Working Model for Interpreting the Excitation Wavelength- and Fluence-Dependent Response in Pulsed Laser-Induced Size Reduction of Aqueous Gold Nanoparticles

Abstract

We propose a model better describing the pulsed laser-induced size reduction of gold nanoparticles in aqueous solution. A numerical simulation was carried out for energy deposition processes initiated by laser excitation on the basis of the two-temperature model (TTM) of electron temperature Te, lattice temperature Tl, and the temperature of the medium surrounding the particle. Further improvement was made by rigorous treatments of electron−phonon dynamics, heat losses, and the optical effect of water bubbles surrounding the nanoparticles due to the temperature rise. The most striking effect was brought about through bubble formation by a nanosecond laser pulse irradiation during which a remarkable decrease in the absorption cross section of gold particles takes place, especially in the spectral region of the surface plasmon resonance band. The calculation allowed the clear classification of two mechanisms (the Coulomb explosion and photothermal mechanisms), and a guideline for examining the mechanistic a...