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

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 0.9 cm−1, 2.3×10−3 cm/W and 0.22 cm−1, 1.9×10−4 cm/W, respectively. These values produce temperature changes of about 90 K in gold nano-colloid and 10 K in silver nano-colloid at focus. Thermo optical constants of samples are determined at low and high temperature changes at focus.

► We have produced silver and gold nanocolloid with ablation of their metal foil in pure water and used them as nonlinear media for SPM and Z scan experiments.
► The number of observed rings in SPM experiments equals 6 for gold nano-colloid and 2 for silver nano-colloid implying nonlinear refraction change is more than three times greater in gold nano-colloid than in silver nano-colloid.
► We have shown that temperature changes in gold nano-colloid is more than ten times greater than silver nano-colloid using Z scan experiments.