OP: Ultrafast and Optomechanical Properties of Individual Plasmonic Antennas

题目：理解由金属纳米粒子组件制成的光学天线中的能量弛豫途径金属纳米粒子支持其导带电子响应入射光的集体运动，这种效应被称为表面等离子体共振。当这些纳米粒子彼此接近到小于其直径的距离时，表面等离子体激元就像连接的谐波振荡器一样开始耦合，这使得设计整体光学响应和设计在可见频率范围内工作的天线成为可能，完全类似于无线电频率接收器和发射器。与无线电天线的不同之处在于，其尺寸缩小到几十纳米（10-9米）。虽然等离子体耦合及其用于接收和发射辐射的概念已经得到了很好的理解，但我们对热损耗（即欧姆电阻）的理解（热损耗总是发生在金属中，在与可见光相互作用的纳米颗粒中更为重要）仅限于具有专门设计的等离子体共振的纳米颗粒组件。该项目旨在解决这个问题，并提供详细的见解，纳米粒子天线的整体几何形状如何影响吸收光子的能量松弛，最终产生热量，直接跟随极短激光脉冲激发能量的命运。通过这项工作获得的知识将使潜在地减少热损失成为可能，但更重要的是利用能量松弛动力学对天线几何形状的依赖来设计快速光电开关和调制器。技术描述本提案的目标是确定由不同尺寸和形状的金属纳米颗粒排列的天线几何形状对电子-声子耦合和声学振动的影响。具体而言，该项目将解决以下两个目标：(1)建立电子能量弛豫对纳米粒子天线几何形状和激发表面等离子体模式类型的依赖关系；(2)研究强耦合纳米粒子天线声振动的激发和阻尼机理。为了实现这些目标，电子显微镜将与使用波长可调脉冲的单粒子瞬态消光光谱相结合，以研究相同的单个纳米粒子天线。单粒子光谱技术是必要的，以关联具有不同几何形状的单个纳米粒子天线的光学和结构特性，因为特别是声学振动的阻尼是由外部因素决定的，即纳米粒子尺寸的多分散性。预计所提出的研究结果将详细了解如何设计纳米粒子天线的结构参数，包括周围介质，以优化所需的电子-声子弛豫时间，以及如何利用脉冲发射的声学振动来调制来自天线本身以及位于天线间隙中的量子发射器的光信号。这些研究工作将对理解纳米粒子天线中超快能量弛豫动力学与结构依赖的集体等离子体模式之间的关系做出重要贡献。

Title: Understanding the energy relaxation pathways in optical antennas made from assemblies of metal nanoparticlesNon-Technical DescriptionMetal nanoparticles support the collective motion of their conduction band electrons in response to incident light, an effect known as a surface plasmon resonance. When those nanoparticles approach each other to within distances of less than their diameters, the surface plasmons start to couple just like connected harmonic oscillators, making it possible to engineer the overall optical response and design antennas that operate in the visible frequency range in complete analogy to radio frequency receivers and transmitters. The difference to radio antennas is that the dimensions are reduced to tens of nanometers (10-9 meter). While this concept of plasmon coupling and its use to receive and transmit radiation is fairly well understood, our understanding of heating losses (i.e. Ohmic resistance), which always occur in metals and are even more important in nanoparticles interacting with visible light, is limited for assemblies of nanoparticles with specifically designed plasmon resonances. This project aims to address this question and to provide detailed insight into how the overall geometry of the nanoparticle antenna affects the energy relaxation of absorbed photons that eventually produce heat by directly following the fate of the excitation energy with very short laser pulses. The knowledge gained through this work will make it possible to potentially minimize heating losses, but also and more importantly exploit the dependence of the energy relaxation dynamics on the antenna geometry to design fast opto-electronic switches and modulators.Technical DescriptionThe goal of this proposal is to determine the effect of the geometry of antennas made from different arrangements of metal nanoparticles that have various sizes and shapes on the electron-phonon coupling and acoustic vibrations. Specifically, the proposed project will address the following two objectives: (1) Establish the dependence of electronic energy relaxation on the nanoparticle antenna geometry and the type of the excited surface plasmon mode; and, (2) Investigate the mechanism for the excitation and damping of acoustic vibrations of strongly coupled nanoparticle antennas. To accomplish these goals, electron microscopy will be combined with single-particle transient extinction spectroscopy employing wavelength tunable pulses to investigate the same individual nanoparticle antennas. Single-particle spectroscopy techniques are necessary to correlate the optical and structural properties of individual nanoparticles antennas having different geometries because especially the damping of the acoustic vibrations is otherwise determined by extrinsic factors, i.e. nanoparticle size polydispersity. It is expected that the outcomes of the proposed studies will yield a detailed insight into how the structural parameters of a nanoparticle antenna, including the surrounding medium, can be engineered to optimize desired electron-phonon relaxation times and how impulsively launched acoustic vibrations can be exploited to modulate the optical signal from the antenna itself as well as quantum emitters located in the antenna gaps. These research efforts will lead to important contributions toward understanding the relationship between the ultrafast energy relaxation dynamics and the structure dependent collective plasmon modes in nanoparticle antennas.