Attosecond Time-Resolved Quantum Dynamics: From Atoms Towards Nanostructures

在过去的十年里，时间分辨光电子能谱领域取得了非凡的进展，使得对简单原子的研究具有了前所未有的电子在原子内运动的时间分辨率，分辨率接近1阿秒（1阿秒是十亿分之一秒的十亿分之一）。该项目将这些研究扩展到更复杂的目标，如吸附物覆盖的固体表面和纳米颗粒。在物质中电子运动的自然时间尺度上，对原子和复杂目标的电子发射动力学的研究涉及到既有研究领域和新兴技术领域。对物质中电子动力学的时间分辨研究将促进对以下方面的全面理解：(1)基本物理过程，如单电子和集体电子激发；(2)金属、半导体、催化表面、（生物）分子和纳米颗粒中的电子和电场动力学。因此，这些研究项目有可能加深我们对表面光化学过程和化学反应动力学的认识。它们具有很强的教育成分，培养学生和博士后在现代原子、光学、表面和计算物理中应用概念以及数学和数值技术。我们的研究成果可能会对新兴技术产生变革性影响，例如超快光波计算、纳米催化和人工光合作用，从而有助于开发新型超快计算机和有效的催化装置，以确保我们的能源供应。阿秒条纹光谱学已经导致了令人印象深刻的时间分辨原子电离研究，并有望显著推进我们对分子、层状半导体结构和纳米颗粒的电子特性的理解。然而，条纹光谱的详细物理解释面临着重大的概念挑战，需要全面的理论研究，即使是简单的原子系统。对于复杂的系统，在描述分子和固体中的瞬态光激发电子动力学时，必须克服额外的严重技术困难。本研究解决了这些挑战，并着重于原子，吸附物覆盖的金属表面和纳米颗粒的时间分辨光发射的建模。为了系统地分析(i)电子相关，（ii）电子传播和（iii）集体电子激发和弛豫效应在光电过程中和之后的作用，它检查了条纹光电光谱。我们将开发和应用互补的量子力学方法：时间相关Schrödinger方程的精确数值解和物理上更透明的解析（S-矩阵）量子力学方法。表面和纳米粒子的有效势将基于密度泛函理论建模。它们将作为强红外和XUV光脉冲与物质相互作用期间电子动力学的完整三维计算的输入。新的数值方法将被探索和实施，允许越来越复杂的样品建模。此外，我们将评估条纹光电子能谱在多大程度上可以揭示(a)固体和固体界面中的电子力和动力学以及(b)非？均匀纳米等离子体电场增强对入射红外条纹脉冲的响应。在数值模拟的支持下，阿秒时间分辨测量为复杂系统中制备、探测和控制电子激发以及化学键的形成和断裂提供了新方法。

Over the past decade, extraordinary advances in the field of time-resolved photoelectron spectroscopy have enabled investigations of simple atoms with an unprecedented time resolution of the electron motion within the atoms, resolution that approaches one attosecond (one attosecond is a billionth of a billionth of a second). This project extends these investigations to more complex targets, such as adsorbate-covered solid surfaces and nanoparticles. These investigations of the dynamics of electron emission from atoms and complex target at the natural time scale of the electronic motion in matter relates to both established and emerging fields of research and technology. Time-resolved studies of the electronic dynamics in matter will promote the comprehensive understanding of i) elementary physical processes, such as single-electron and collective electronic excitations and ii) the dynamics of electrons and electric fields in metals, semiconductors, and catalytic surfaces, (bio-) molecules, and nanoparticles. These research projects are thus likely to deepen our insight into photochemical processes and chemical reaction dynamics at surfaces. They have a strong educational component by training students and postdocs in applying concepts as well as mathematical and numerical techniques used in modern atomic, optical, surface, and computational physics. Our research efforts may have a transformative impact on emerging technologies, such as ultrafast light-wave computing, nanocatalysis, and artificial photosynthesis, thereby contributing to the development of novel ultrafast computers and efficient catalytic devices needed to secure our energy supply.Attosecond streaking spectroscopy has led to impressive time-resolved studies of atomic ionization and is anticipated to significantly advance our understanding of electronic properties of molecules, layered--semiconductor structures, and nanoparticles. However, the detailed physical interpretation of streaked spectra faces significant conceptual challenges and necessitates comprehensive theoretical investigations, even for simple atomic systems. For complex systems, additional severe technical difficulties in describing the transiently photoexcited electronic dynamics in molecules and solids must be overcome. This research addresses these challenges and focuses on the modeling of time-resolved photoemission from atoms, adsorbate-covered metal surfaces, and nanoparticles. It examines streaked photoemission spectra in order to systematically analyze the role of (i) electronic correlation, (ii) electron propagation, and (iii) collective electronic excitation and relaxation effects during and after the photoemission process. We will develop and apply complementary quantum--mechanical methods: exact numerical solutions of the time--dependent Schrödinger equation and physically more transparent analytical (S--matrix) quantum-mechanical methods. Effective potentials for surfaces and nanoparticles will be modeled based on density-functional theory. They will serve as input for full three--dimensional calculations of the electronic dynamics during the interaction of intense IR and XUV light pulses with matter. New numerical methods will be explored and implemented, allowing for the modeling of increasingly complex samples. Furthermore, we will assess the degree to which streaked photoelectron spectroscopy can reveal information on (a) electronic forces and dynamics in solids and at solid interfaces and (b) non?homogenous nanoplasmonic electric--field enhancements in response to an incident IR streaking pulse. Supported by numerical modeling, attosecond time-resolved measurements promise novel methods to prepare, probe, and control electronic excitations and the formation and breaking of chemical bonds in complex systems.