Surface plasmon enhanced third-order optical nonlinearity of silver nanocubes

We present the linear and nonlinear optical properties of Ag nanocubes. The surface plasmon resonance absorption peak shows a red shift with increasing cube size. The nonlinear absorption and nonlinear refraction were measured by using Z-scan technique. The Ag nanocubes with the edge size of 60 nm show the largest third-order optical nonlinearity, which is supported by the largest field enhancement factor through the FDTD simulations. In the wavelength range from 720 nm to 920 nm, the one-photon and two-photon figures of merit, W and T satisfy the demand of W > 1 and T < 1, which implies it is a promising candidate for the optical switching devices.