Agiotis Leonidas, Meunier Michel
Opt Express. 2021 Nov 22;29(24):39536-39548. doi: 10.1364/OE.441117.
We evaluate the threshold power for self-focusing in gold nanorod colloids of varying concentration by a power limiting method in the femtosecond filamentation regime. The pulses are tuned near the longitudinal plasmon peak of the nanorods, leading to saturation of linear absorption and reshaping of the particles. We evaluated the last two effects by optical transmission measurements and spectroscopic analysis and estimated that considerable particle deformation does not occur before the collapse of the beam. We performed numerical simulations based on the experimental results, and evaluated only a subtle, monotonically increasing enhancement of the nonlinear refractive index of the host material (water) as the nanoparticles concentration increases. The role of higher-order contributions is discussed. Our work provides an alternative characterization approach of ultrafast nonlinearities in absorbing media. It further emphasizes that self-focusing of intense femtosecond pulses in gold nanocomposites is hampered by the ultrafast modulation of the susceptibility of the metal.
我们通过飞秒成丝区域的功率限制方法，评估了不同浓度金纳米棒胶体中自聚焦的阈值功率。脉冲被调谐到纳米棒纵向等离子体峰附近，导致线性吸收饱和以及粒子重塑。我们通过光透射测量和光谱分析评估了后两种效应，并估计在光束坍缩之前不会发生显著的粒子变形。我们基于实验结果进行了数值模拟，并且仅评估了随着纳米粒子浓度增加，主体材料（水）的非线性折射率有细微的、单调增加的增强。讨论了高阶贡献的作用。我们的工作提供了一种吸收介质中超快非线性的替代表征方法。它进一步强调，金纳米复合材料中强飞秒脉冲的自聚焦受到金属极化率超快调制的阻碍。
