Strategies for the ultrafast optical control of magnetism have been a topic of intense research for several decades because of the potential impact in technologies such as magnetic memory¹, spintronics² and quantum computation, as well as the opportunities for nonlinear optical control and modulation³ in applications such as optical isolation and non-reciprocity⁴. Here we report experimental quantification of optically induced magnetization in plasmonic gold nanoparticles due to the inverse Faraday effect. The induced magnetic moment is large under typical ultrafast pulse excitation (<10¹⁴ W m⁻² peak intensity), with magnetization and demagnetization kinetics that are instantaneous within the subpicosecond time resolution of our study. Our results support a mechanism of coherent transfer of angular momentum from the optical field to the electron gas, and open the door to all-optical subwavelength strategies for optical isolation that do not require externally applied magnetic fields.

由于对诸如磁存储器¹，自旋电子²，量子计算等技术的潜在影响以及非线性光学控制和调制³的机会，磁的超快光学控制策略已成为数十年来研究的热点。光学隔离和不可逆等应用⁴。在这里，我们报告由于反法拉第效应，在等离激元金纳米粒子中光诱导磁化的实验量化。在典型的超快脉冲激励下（<10 ¹⁴  W m ^-2峰值强度），并且在我们研究的亚皮秒时间分辨率内具有瞬时的磁化和退磁动力学。我们的研究结果支持了角动量从光场到电子气的相干传递机制，并为不需要外部施加磁场的全光亚波长光隔离策略打开了大门。