Thermo optical properties of Ag nanoparticles produced by pulsed laser ablation

The linear and nonlinear optical properties of silver nanoparticles have been investigated experimentally. Colloidal nanoparticle samples were synthesized by laser ablation at various fluences. The samples were characterized by linear absorption spectroscopy, transmission electron microscopy and dynamic light scattering methods. The behavior of nonlinear refractive index of nanoparticles was studied using the close and open Z-scan techniques by low power CW laser beam. Observation of asymmetrical configurations of the Z-scan curve indicates that nonlinear refraction occurring in the Ag samples is related to the thermo optical process. In addition, the observed optical limiting behavior is due to nonlinear refraction of samples arising from thermal lens formation under low power CW excitation. The optimum position for samples as the optical limiter based on self-defocusing effect is the valley point. When the illumination laser power is low, the self-defocusing effect is mainly dominated. Actually laser fluence variation during the ablation procedure leads to concentration variation of nanoparticles in suspensions which in turn affect the optical properties of samples. The dependence of the nonlinear properties on morphological parameters, metal concentration, and particle size have been explained by experimental results.