Effect of concentration and particle size on nonlinearity of Au nano-fluid prepared by γ (60Co) radiation

Nonlinear properties of Au nano-fluid prepared by γ-radiation method at different concentrations were investigated. Measurements of nonlinear refractive index and nonlinear absorption coefficient were carried out using a single beam Z-scan technique. A green CW laser beam operated at 532 nm was used as excitation source. The Au nano-fluid shows a good third order nonlinear response. The sign of the nonlinear refractive index is found to be negative and the magnitude is in the order of 10−7 cm2/W. This nonlinear effect increases as the concentration increases from 3.119 × 10−4 to 2.354 × 10−3 M which correspond to particle sizes of 4.0–30.5 nm, respectively. A good linear relationship was obtained between nonlinear refractive index and concentration. However the relationship between nonlinear refractive index and particle size was nonlinear behavior.