Effect of the composition of AuxAg(1−x) nanoalloys on their nonlinear optical response

In the present work the nonlinear optical response of some Au_xAg_(1-x) alloy nanoparticles (NPs) prepared by a femtosecond laser ablation process is studied using Z-scan technique employing 4 ns, 532 nm laser pulses. The prepared NPs with diameters of 15 - 20 nm, had different compositions, i.e. gold molar fractions (GMF) x, ranging from x = 0 (pure Ag) to x = 1 (pure Au) and they were exhibiting surface plasmon resonance (SPR) peak whose spectral position and strength were varying depending on GMF. The Au_xAg_(1-x) NPs were found to exhibit negative nonlinear refraction, corresponding to self-defocusing behavior and negligible nonlinear absorption. The nonlinear optical response of the Au_xAg_(1-x) alloy nanoparticles was found to be strongly dependent on the GMF of the nanoalloy, since the surface plasmon resonance peak enhances the nonlinear optical response of the metallic nanoalloys when it is close to the excitation wavelength.