Nonlinear optical effects from Au nanoparticles prepared by laser plasmas in water

The optical limiting properties of Au nanoparticles prepared by laser generated plasmas in water were investigated. The ablation processes were carried out irradiating an Au target with the second harmonic (532 nm) output of a Nd:YAG laser, changing the water level above the target, the lens position and the laser pulse energy. Different surface morphologies, from isolated nearly spherical nanoparticles to elongated structures, were observed by TEM imaging. A significant nonlinear optical response was probed by the Z-scan technique. The efficiency and the nature of the nonlinear response are found to be strongly dependent on the morphological properties of the nanostructures. The third order optical susceptibility χ(3) assumes the values of 1.83 × 10−6 esu and 6.34 × 10−6 esu for the smaller nanoparticles size obtained at the lower ablation energies (10–20 mJ), 8.25 × 10−6 esu and 2.13 × 10−5 esu for the particles agglomerations obtained at the higher ablation energies (50–100 mJ). The high value of χ(3) and the possibility to tailor the nonlinear optical response by changing the morphological properties of the Au nanostructures make them interesting materials for potential applications in the nonlinear optics field.