Probing and Controlling Electronic Dynamics in Matter with Atomic Spatiotemporal Resolution

光电子发射是自然界中光与物质相互作用的基本过程。它发生在具有足够短波长和足够强度的电磁辐射入射到物质上时，通过入射辐射与电子的耦合进行，并导致光子能量转移到目标的内部激发和电子的发射。所发射的光电子携带关于靶材料的光发射动力学和电子性质的信息。世纪以来，对它们的能量和动量分布的测量和分析一直是确定物质电子结构的最丰富的方法之一，重要地促进了激光和探测技术以及精确的量子力学理论方法的发展。能量域光谱图像的样品的时间平均的内部电子动力学过程中的光电发射过程中，但不解决超快的时间依赖的电子动力学过程中的光电子释放（或重新散射）。提出的理论工作的动机是超快激光技术的非凡进步，使超短光脉冲的产生及其精确的控制和同步。这些脉冲允许研究孤立原子和凝聚态系统中的电子动力学，具有物质中电子运动的自然时间尺度的时间分辨率和原子空间分辨率。就像拍摄一个快速移动的物体的电影一样，比如飞行中的子弹，需要许多帧的频闪组合，每个帧构成物体的瞬时图像，时域光谱学即将提供“电子电影”，能够以原子时空分辨率显示电子在物质中的运动和它们的发射。拟议的研究将促进我们对（i）单电子和集体电子激发的理解，以及（ii）层状半导体，吸附物覆盖的表面和纳米颗粒中电子和场的动力学，促进新兴技术，如光波计算，纳米催化和人工光合作用，从而有助于开发新型计算机和催化装置，以确保我们的能源供应和保护我们的环境。阿秒时间分辨光谱学已经导致了令人印象深刻的时间-领域的电离过程的研究孤立的（气态）原子，并预计将显着推进我们的层状半导体结构和纳米粒子的电子特性的理解。然而，时间分辨光电子能谱的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，如纳米粒子和固体表面，在描述瞬态光激发电子动力学的额外严重的技术困难，必须克服。拟议的工作应对这些挑战。它侧重于模拟时间和空间分辨的电子发射和产生的上转换高谐波（HH）辐射从吸附物覆盖的金属表面和纳米粒子。它通过发展和应用互补的量子力学方法，包括含时薛定谔方程的数值解，以及物理上更透明的半经典方法来进行。它将评估时间和发射角分辨光电子和HH光谱可以揭示（a）固体中的电子力和动力学信息以及（B）入射光脉冲的非均匀纳米等离子体电场增强的保真度。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Photoelectron emission is a fundamental light-matter interaction process in nature. It occurs upon the incidence of electromagnetic radiation with sufficiently short wavelength and adequate intensity on matter, proceeds through the coupling of the incident radiation with electrons, and results in the transfer of photonic energy to internal excitations of the target and the emission of electrons. The emitted photoelectrons carry information about the photoemission dynamics and electronic properties of the target material. For more than a century, the measurement and analysis of their energy and momentum distribution has been one of the most prolific methods for determining the electronic structure of matter, importantly promoting the development of laser and detection technologies as well as accurate quantum-mechanical theoretical methods. Energy-domain spectra image the sample's time-averaged internal electronic dynamics during the photoemission process, but do not resolve the ultrafast time-dependent electronic dynamics during the photoelectron-release (or –rescattering) process. The proposed theoretical work is motivated by extraordinary progress in ultrafast laser technology that enabled the generation of ultrashort light pulses and their accurate control and synchronization. These pulses allow for investigations of the electronic dynamics in isolated atoms and condensed matter systems with temporal resolution at the natural timescale of the electronic motion in matter and with atomic spatial resolution. In the same way as making a movie of a fast-moving object, such as a bullet in flight, requires the stroboscopic assembly of many frames, each constituting a momentary image of the object, time-domain spectroscopy is about to provide “electronic movies”, capable of displaying the motion of electrons in and their emission from matter with atomic spatiotemporal resolution. The proposed studies will advance our understanding of (i) single--electron and collective electronic excitations and (ii) the dynamics of electrons and fields in layered semiconductors, adsorbate-covered surfaces, and nanoparticles, promoting emerging technologies, such as light-wave computing, nano-catalysis, and artificial photosynthesis, thereby contributing to the development of novel computers and catalytic devices for securing our energy supply and preserving our environment.Attosecond time-resolved spectroscopy has led to impressive time-domain studies of ionization processes on isolated (gaseous) atoms and is anticipated to significantly advance our understanding of electronic properties of layered-semiconductor structures and nanoparticles. However, the physical interpretation of time-resolved photoemission spectra faces significant conceptual challenges and necessitates comprehensive theoretical investigations, even for simple atomic systems. For complex systems, such as nanoparticles and solid surfaces, additional severe technical difficulties in describing the transiently photoexcited electronic dynamics must be overcome. The proposed work addresses these challenges. It focuses on the modeling of time- and spatially resolved emission of electrons and the generation of up-converted high-harmonic (HH) radiation from adsorbate-covered metal surfaces and nanoparticles. It proceeds by developing and applying complementary quantum-mechanical methods, including numerical solutions of the time-dependent Schrödinger equation, and physically more transparent semi-classical methods. It will assess the fidelity with which time- and emission-angle-resolved photoelectron and HH spectra can reveal information on (a) electronic forces and dynamics in solids and (b) non-homogenous nano-plasmonic electric-field enhancements of incident light pulses.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.