Harmonic generation in metallic nanoscale systems

The nonlinear interaction between materials based on metallic nanoparticles and strong electric fields such as the one produced by laser pulsed radiation produces significant response amplification whenever system resonances are being excited. In particular, second harmonic radiation excited by pulsed lasers in the near infrared can be generated in these systems with efficiencies far exceeding those of corresponding bulk materials. In this paper, experimental results are presented for two different 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 different geometries and their dependence on various physical parameters illustrate the central role of surface plasmon resonances. This experimental evidence is reasonably corroborated by ad hoc models.