Off-Resonant Third-Order Optical Nonlinearity of an Ag:TiO2Composite Film

Abstract

Using the femtosecond time-resolved optical Kerr effect technique, weinvestigate the off-resonant nonlinear optical response of anAg:TiO2 composite film prepared by a vacuum magnetron sputteringmethod. The third-order nonlinear optical susceptibility of thecomposite film with silver nanoparticle size of about 30 nm isestimated to be 1.9×10−10 esu at the incident laser wavelength of800 nm. When the photon energy of the incident beam is lower than thatfor surface plasmon or the interband transition of silvernanoparticles, the observed third-order optical nonlinearity isattributed to the intraband transition of the free electrons. Based onthe linear limit of the electric field within micro-spherical model, weassign this large optical nonlinearity to the local field enhancementof the third-order nonlinearity.