Plasmon Enhanced Optical Magnetism in Metal Nanostructures

这项研究探讨了用光产生和控制磁场的策略。磁性是光与金金属相互作用的结果。虽然金金属在黑暗中没有磁性行为，而且光通常不会产生稳定的磁场，但该系统的两个特征使光致磁性成为可能。首先，金以非常小的颗粒形式制备，称为纳米颗粒，比光的波长小得多。由于其小尺寸，金纳米颗粒具有极大地集中和增强光吸收的独特能力。其次，光是圆偏振的，这意味着光束也会引起金属纳米颗粒中电子的旋转运动。这些综合效应在纳米颗粒中产生大的循环电流，反过来又产生磁场。每个纳米粒子的行为就像一个小的，非常强大的磁铁。磁场只在灯光闪烁时存在，因此磁性可以像灯光一样快速地打开和关闭。通过更好的理解，这种行为可以允许比当前计算机存储器系统更小和更快的磁切换，这些存储器系统将信息存储在可切换的磁体中。这项工作也支持学生培训科学交流到non-technical audiers.This研究分析了光学，磁性和热行为，从共振增强的相干，旋转电荷位移等离子体金属纳米结构在圆偏振光激发过程中的结果。由于圆偏振光场的角动量的直接转移而在物质中产生磁场被称为逆法拉第效应，并且是这些实验中研究的中心焦点。逆法拉第效应进行了分析，使用时间分辨泵浦-探测光谱和连续波光谱上的胶体悬浮液的金纳米粒子，旨在提供入射光场的等离子体增强。实验的重点是区分光致磁性从其他非线性光学现象，如光学克尔效应，或非相干热化过程。这些实验还量化了光致磁性的幅度、频率依赖性、时间响应和微观机制，以阐明超快、超快、超快该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的评估被认为值得支持。影响审查标准。

This research examines strategies for generating and controlling magnetic fields with light. The magnetism is the result of an interaction of light with gold metal. Although gold metal has no magnetic behavior in the dark, and light does not usually generate stable magnetic fields, two features of this system enable light-induced magnetism. First, the gold is prepared in the form of very small particles, called nanoparticles, that are much smaller than the wavelength of light. Because of their small size, gold nanoparticles have a unique ability to greatly concentrate and enhance the absorption of light. Second, the light is circularly polarized, meaning that the beam of light also causes rotational motion of electrons in the metal nanoparticles. These combined effects produce large circulating electric currents in the nanoparticles that, in turn, give rise to magnetic fields. Each nanoparticle behaves like a small, very strong magnet. The magnetic field is only present when the light is shining, so the magnetism can be switched on and off as quickly as the light can be turned on and off. With better understanding, this behavior can allow for even smaller and faster magnetic switching than current computer memory systems that store information in switchable magnets. This work also supports student training in scientific communication to non-technical audiences.This research analyzes the optical, magnetic, and thermal behavior that results from resonant enhancement of coherent, rotating charge displacement in plasmonic metal nanostructures during excitation with circularly polarized light. The generation of magnetic fields in matter due to the direct transfer of angular momentum from circularly polarized optical fields is termed the inverse Faraday effect, and is the central focus of study in these experiments. The inverse Faraday effect is analyzed using both time-resolved pump-probe spectroscopy and continuous wave spectroscopy on colloidal suspensions of gold nanoparticles that are designed to provide plasmonic enhancement of the incident optical field. Experiments are focused on distinguishing optically-induced magnetism from other non-linear optical phenomena, such as the optical Kerr effect, or non-coherent thermalization processes. The experiments also quantify the magnitude, frequency dependence, time response, and microscopic mechanism of the optically-induced magnetism, in order to elucidate new avenues of optoelectronic and opto-magnetic functionality in nanostructures enabled by ultrafast, optically modulated magnetic field generation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.