Second-order nonlinear response of composites containing aligned elongated silver nanoparticles.

We present second-harmonic generation (SHG) measurements and simulations from a silica matrix containing randomly distributed but aligned elongated silver nanoparticles (NPs). The composites were produced by a double ion-implantation process of silver nanoparticles followed by an irradiation with Si ions. It is demonstrated that one can model the experimental results by considering the sub-micrometric composite layer as a nonlinear media containing rod NPs for which the hyperpolarizability tensor is cylindrically symmetric along the NP long axis. The second-order macroscopic susceptibility of the composite originates from the coherent summation of the hyperpolarizabilities associated to each NP. We obtain analytical expressions for the p- and s-polarized effective susceptibility tensor as a function of experimental variables, such as the fundamental beam input polarization and sample orientation, and fitting parameters relating the cylindrically shaped hyperpolarizability. In addition, coherent SHG measurements on spherical nanoparticles resulting from the first ion-implantation process are also presented showing an isotropic polar behavior for the total SHG intensity where the p-polarized SHG intensity resulted to be the main contribution.