Determining the nonlinear coefficient of gold and silver nano-colloids using SPM and CW Z-scan

Abstract

Nonlinear and thermo optical properties of the gold and silver nano-colloids were investigated using CW Z-scan experiments. Sign of nonlinear refraction coefficient of colloids are negative at this condition. Negative sign implying thermal self defocusing is the most important mechanism of nonlinearity in our experiments. Diffraction pattern shows that nonlinear refraction of gold nano-colloid must be at least three times greater. The linear and nonlinear absorption coefficients of gold nano-colloid and silver nano-colloid is determined to be 0.9cm−1, 2.3×10−3cm/W and 0.22cm−1, 1.9×10−4cm/W, respectively. These values produce temperature changes of about 90K in gold nano-colloid and 10K in silver nano-colloid at focus. Thermo optical constants of samples are determined at low and high temperature changes at focus.