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

Nonlinear properties of Au nano-fluid prepared by gamma-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) cm(2)/W. This nonlinear effect increases as the concentration increases from 3.119 x 10(-4) to 2.354 x 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. (C) 2010 Elsevier B.V. All rights reserved.