Attosecond Electron Dynamics

在这个由化学系化学结构动力学和机制-A（CSDM-A）项目资助的项目中，加州伯克利大学的Stephen Leone教授正在使用创新的激光技术在尽可能短的时间内研究分子的行为。 这些实验检测到的快速分子变化的时间尺度低至数百阿秒（1阿秒是十亿分之一秒的十亿分之一）。 由于用激光产生阿秒光脉冲的新方法，这种测量在过去15年才成为可能。 由于电子运动如此之快，它们的运动（电子动力学）成为所研究的分子过程的中心。 这项研究测量了快速电子运动，例如当电荷在分子中重新分布或周期性变化时，或者电子随着分子结构的变化而跳跃。 为了实现这一目标，Leone教授产生了两个激光脉冲，一个用于激发分子，另一个延迟时间以测量分子反应，类似于比赛中的发令枪和秒表。这些实验使用多种光学技术来获得所需的短脉冲和精确的时间延迟。预计社会将从测量能力的发展中受益，这些能力将使用需要精确稳定性的工具来推动时间的界限。 随着设备尺寸的减小以及存储介质和计算工具的性能速度的增加，这些技术是重要的。参与该项目的学生正在学习一系列与高科技专业相关的技术和原理，包括激光技术、电子学和计算。阿秒时间分辨测量代表了一种新的方法，可以在足够短的时间尺度上探测化学动力学，从而将电子动力学与核运动分开。电子相关和电子叠加态等电子动力学在这些短时间尺度上的化学过程中起着核心作用，电子和原子核之间的时间尺度可分离性的破坏也是如此（玻恩·奥本海默）。为了研究这些现象，一个实验室的基础上生产孤立的阿秒脉冲在极紫外（XUV）光谱范围内。化学系统涉及测量电子叠加、解离过程和通过电子激发分子的曲线交叉或圆锥交叉的几飞秒和亚飞秒（阿秒）时间动力学。 参与这个基于阿秒测量的项目的学生正在获得高科技行业新兴领域的各种经验。这些包括，例如，载波包络相位稳定的激光器，光的干涉控制，核心水平光谱学原理，X射线光学编程，电子光谱仪和速率方程方法来预测电离，轨道占有率和对齐。

In this project funded by the Chemical Structure Dynamics and Mechanism-A (CSDM-A) program of the Chemistry Division, Professor Stephen Leone of the University of California Berkeley is using innovative laser techniques to investigate the behavior of molecules at the shortest possible time. The experiments detect fast molecular changes on timescales down to hundreds of attoseconds (1 attosecond is one billionth of a billionth of a second). Such measurements have only become possible in the last 15 years due to new methods for producing attosecond light pulses with lasers. Because electrons move so rapidly, their motion (electron dynamics) becomes central to the molecular processes under investigation. This research measures fast electron motion, such as when charges redistribute or periodically change in molecules, or electrons hop as the structure of the molecule transforms. To accomplish this, Professor Leone produces two laser pulses, one to excite the molecules and one delayed in time to measure the molecular response, analogous to a starting pistol and a stopwatch in a race. These experiments use numerous optical technologies to obtain the required short pulses and accurate time delays. The benefits to society are anticipated from the development of measurement capabilities that push the boundaries of time using tools that require precision stability. These techniques are important as the dimensions of devices decrease and performance speeds of storage media and computational tools increase. The students engaged in this project are learning an array of techniques and principles relevant for high technology professions, including laser technology, electronics, and computing.Attosecond time-resolved measurements represent a new way to probe chemical dynamics on timescales short enough to separate electron dynamics from nuclear motion. Electron dynamics such as electron correlation and electronic superposition states play a central role in chemical processes on these short timescales, as does the breakdown of the separability of timescales between electrons and nuclei (Born Oppenheimer). To study these phenomena, an experimental laboratory based on the production of isolated attosecond pulses in the extreme ultraviolet (XUV) spectral range is employed. The chemical systems involve measurements of few-femtosecond and subfemtosecond (attosecond) time dynamics of electronic superpositions, dissociation processes, and passage through curve crossings or conical intersections of electronically excited molecules. The students involved in this attosecond measurement-based project are gaining experience in a variety of areas that are emerging in high tech industry. These include, for example, carrier-envelope-phase stabilized lasers, interferometric control of light, core level spectroscopy principles, x-ray optical programming, electron spectrometers, and rate equation approaches to predict ionization, orbital occupancy, and alignment.