Nonlinear optical response of colloidal gold nanoparticles studied by hyper-Rayleigh scattering technique

Hyper-Rayleigh scattering (HRS) technique is used to study the nonlinear op tical response of nanocrystalline gold particle suspensions. The signal int ensity measured at 400 nm has a cubic dependence on the pump laser energy a t 1064 nm, indicating that the measured signal is due to a third-order nonl inear optical process, namely three-photon excited fluorescence (3PF). To t he best of our knowledge, this is the first experimental observation of 3PF for colloidal gold nanoparticle suspensions.