Accurate determination of nonlinear refraction in ZnO and Au composite nanostructures

It is now well established that the nonlinear optical properties of ZnO nanoparticles can be significantly enhanced by coupling them to metallic nanoparticles. While the nonlinear absorption properties are well reported, there is large variation in the coefficients of nonlinear refraction reported in literature, largely due to simplifications made during the analysis of experimental z-scan data used to determine the coefficients. This work presents closed aperture z-scan theory which incorporates the effects of nonlinear absorption, thus providing a more accurate measure of the coefficient of nonlinear refraction. With this theory, it is shown that the coefficient of nonlinear refraction increases by an order of magnitude when ZnO is coupled to Au nanoparticles.