Using femtosecond laser pulses to investigate the nonlinear optical properties of silver nanoparticles colloids in distilled water synthesized by laser ablation

The nonlinear optical properties of silver nanoparticles (AgNPs) colloids in distilled water, when irradiated with 100 fs laser pulses, were investigated experimentally using the Z-scan technique. At a constant wavelength of 760 nm and different excitation powers, the nonlinear absorption coefficient and nonlinear refractive index were measured. The AgNPs colloids are synthesized by laser ablation of silver bulk in distilled water using a 532 nm Nd: YAG laser with different ablation energies fluence of 9, 15.5, and 26x10(4) (J/cm(2)) over a 30min ablation time. The nanoparticle size, shape, and absorption spectra of nanoparticle colloids were determined using transmission electron microscopy and an ultraviolet-visible spectrophotometer. Spherical AgNPs are formed with an average diameter ranging from 7.5 to 12 nm. As the laser ablation energy fluence increases, the average size of the AgNPs decreases while the bandgap energy increases. As the excitation laser power and AgNPs size increase, the nonlinear absorption coefficient and nonlinear refractive index decrease. The optical limiting performance of AgNPs improves with increasing laser ablation energy fluence, with the best performance at 26x10(4) (J/cm(2)).