Understanding metal nanoparticles optical behavior: a case study

The nonlinear interaction between materials based on metallic nanoparticles and strong electric ¯elds such as the one produced by laser pulsed radiation produces signi¯cant response ampli¯cation whenever electronic or photonic system resonances are being excited. In particular, second harmonic radiation excited by pulsed lasers in the near infrared can be generated in metal nanoparticles with e±ciencies far exceeding those of corresponding bulk materials. In this paper, experimental results are presented for two di®erent physical systems, namely Au nanoparticles in aqueous solutions and Ga nanoparticle monolayers embedded in dielectric matrices with mean radii in the nanometer range. Measurements of second harmonic generated radiation in the two systems in di®erent geometries and their dependence on various physical parameters shed light on the response mechanisms to electromagnetic radiation.