Second-Harmonic Scattering from Metallic Nanoparticles in a Random Medium

We report the second-harmonic scattering intensity from silver nanoparticles dispersed in a linear random medium. The medium is formed by an aqueous solution of 80 nm diameter silver nanoparticles acting as nonlinear optical sources and 200 nm diameter latex nanospheres used as scattering centers. At photon scattering mean free paths longer than the ballistic photon path length, the second-harmonic intensity decreases exponentially due to the linear scattering of both the fundamental and harmonic beams. However, below a critical photon scattering mean free path, the decrease of the nonlinear optical intensity levels off. Polarization analysis further provides details about the transition from the ballistic to scattered second-harmonic photons. Because of the incoherent nature of the second-harmonic scattering process, we suggest that a lengthening of the interaction time of the fundamental photons with the nonlinear medium occurs.