Intensity-Dependent Optical Absorption of Colloidal Solutions of Gold Nanoparticles

Intensity-dependent absorption measurements for determining the non-linear optical susceptibility of aqueous colloidal solutions of gold nanoparticles are presented. The diameters of the gold particles ranged from 50 to 400 Å. Measurements were performed in the vicinity of the surface plasmon resonance frequency and the resonantly enhanced susceptibility was found to be of the order of 5 · 10 -16 m 2 V -2 . This is attributed to a change in the Fermi-Dirac distribution of electrons about the Fermi level and is caused by an increase in their temperature due to absorption of resonant photons. The intensity dependence of the absorption showed that the system can be described as inhomogeneously broadened.