OP: Ultrafast and Optomechanical Properties of Individual Plasmonic Antennas

标题：了解由金属纳米颗粒组装而成的光学天线中的能量弛豫路径非技术描述金属纳米颗粒支持其导带电子在入射光下的集体运动，这种效应被称为表面等离子体共振。当这些纳米粒子相互靠近，距离小于它们的直径时，表面等离子体就会开始耦合，就像相连的谐振子一样，这使得设计整体光学响应和设计工作在可见频率范围内的天线成为可能，完全类似于射频接收器和发射器。与无线电天线的不同之处在于，尺寸缩小到几十纳米(10-9米)。虽然等离子激元耦合的概念及其用来接收和发射辐射的概念已经被很好地理解，但我们对热损失(即欧姆电阻)的理解仅限于具有特殊设计的等离子激元共振的纳米粒子的组装。该项目旨在解决这一问题，并详细了解纳米粒子天线的总体几何形状如何影响被吸收光子的能量弛豫，这些光子最终通过用非常短的激光脉冲直接跟随激发能量的命运而产生热量。通过这项工作获得的知识将使潜在地最小化热损失成为可能，而且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的光电开关和调制器。技术描述这项提议的目标是确定由不同尺寸和形状的金属纳米粒子组成的不同排列的天线的几何形状对电子-声子耦合和声振动的影响。具体地说，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激元模式的依赖关系；(2)研究强耦合纳米粒子天线的声振动的激发和衰减机制。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时消光光谱相结合来研究相同的单个纳米粒子天线。单粒子光谱技术对于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是必要的，因为特别是声振动的衰减是由外部因素决定的，即纳米粒子的尺寸多分散性。预计拟议研究的结果将对如何设计纳米颗粒天线的结构参数，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振动来调制来自天线本身以及位于天线缝隙中的量子发射器的光信号产生详细的见解。这些研究工作将为理解纳米粒子天线中的超快能量弛豫动力学与结构相关的集体等离子体激元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.