Surface Plasmon Enhanced Third-Order Nonlinear Optical Effects in Ag-Fe3O4 Nanocomposites

We report an approach to enhance the third-order nonlinear optical properties of a nanocrystal through the attachment of another metallic nanoparticle. Both two-photon absorption (TPA) cross section and nonlinear refractive (NR) cross section of a Fe3O4 nanocube with and without the attachment of an Ag nanoparticle are characterized by using the Z-scan technique. As compared to pristine Fe3O4 nanocube, the TPA and NR cross section of Ag-particle-attached Fe3O4 nanocube is increased by several folds at light frequencies far below the surface plasmon resonance of Ag particle, with precise values depending on the size of the Ag particle. These enhanced values are in agreement with the theoretically calculated enhancement by discrete dipole approximation modeling, which reveals that the local electric field induced by the metal nanoparticle should play an essential role in the enhancement.