Metallic nanoparticles are of great interest in technological applications, especially in photonics. Here, we describe the nonlinear optical properties of colloidal solutions of monometallic silver (AgNPs) and bimetallic nanoparticles, with Ag (core) - Au (shell) (Ag@AuNPs) structure, in the infrared region with ultrashort pulses. UV–Vis spectroscopy showed LSPR (localized surface plasmon resonance) characteristics bands. MEV measurements confirm that the nanoparticles have a spherical shape with good size distribution around 56 nm for AgNPs and 73 nm for Ag@AuNPs. The nonlinear optical properties of the nanostructures were determined by the Z-scan technique, with a laser at 1040 nm (~357 fs), for different intensities. We observed the effects of saturated absorption and reverse saturated absorption as a function of intensity for both nanoparticles with the increase of laser intensity was observed in the open-aperture (OA) measurements in nonresonant mode. Ag@AuNPs present a complete transition from saturation absorption to reverse saturation absorption. The close-aperture (CA) measurements in nonresonant mode indicate an effective negative nonlinearity for nanoparticles, corresponding to self-defocusing. Our results show that these bimetallic nanoparticles have great potential for application in photonics, especially in applications where the tuning of nonlinear optical properties is a determining factor.

金属纳米粒子在技术应用中很受关注，特别是在光子学中。在这里，我们描述了具有 Ag（核）-Au（壳）（Ag@AuNPs）结构的单金属银 (AgNPs) 和双金属纳米粒子的胶体溶液在超短脉冲红外区域的非线性光学特性。UV-Vis 光谱显示出 LSPR（局部表面等离子体共振）特征带。MEV 测量证实纳米粒子具有球形形状，具有良好的尺寸分布，AgNPs 约为 56 nm，Ag@AuNPs 约为 73 nm。纳米结构的非线性光学特性由 Z 扫描技术确定，激光波长为 1040 nm（~357 fs），强度不同。我们观察到饱和吸收和反向饱和吸收作为两种纳米粒子强度的函数，随着激光强度的增加，在非共振模式下的开放孔径 (OA) 测量中观察到的影响。Ag @ AuNPs呈现出从饱和吸收到反向饱和吸收的完全过渡。非共振模式下的小孔径（CA）测量表明纳米粒子有效的负非线性，对应于自散焦。我们的结果表明，这些双金属纳米粒子在光子学中具有巨大的应用潜力，尤其是在非线性光学特性的调整是决定因素的应用中。Ag@AuNPs 呈现从饱和吸收到反向饱和吸收的完全转变。非共振模式下的近孔径 (CA) 测量表明纳米粒子的有效负非线性，对应于自散焦。我们的结果表明，这些双金属纳米粒子在光子学中具有巨大的应用潜力，特别是在非线性光学特性的调整是决定性因素的应用中。Ag@AuNPs 呈现从饱和吸收到反向饱和吸收的完全转变。非共振模式下的近孔径 (CA) 测量表明纳米粒子的有效负非线性，对应于自散焦。我们的结果表明，这些双金属纳米粒子在光子学中具有巨大的应用潜力，尤其是在非线性光学特性的调整是决定因素的应用中。