Attosecond Electron Dynamics

在这个由化学系化学结构动力学和机理A(CSDM-A)计划资助的项目中，加州大学伯克利分校的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。这些实验探测到时间尺度上的快速分子变化，精确到数百阿秒(1阿秒是十亿分之一秒)。由于用激光产生阿秒光脉冲的新方法，这种测量只有在过去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)成为正在研究的分子过程的中心。这项研究测量了电子的快速运动，例如当分子中的电荷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。为了做到这一点，里昂教授产生了两个激光脉冲，一个用来激发分子，另一个用来测量分子反应的时间延迟，类似于比赛中的发令枪和秒表。这些实验使用许多光学技术来获得所需的短脉冲和准确的时间延迟。通过使用要求精度稳定的工具来推动时间界限的测量能力的发展，预计将给社会带来好处。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提高，这些技术变得非常重要。参与这个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、电子学和计算机。秒级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索化学动力学，以将电子动力学和核运动分开。电子动力学，如电子关联和电子叠加态，在这些短时间尺度上的化学过程中发挥着核心作用，电子和原子核之间时间尺度的可分离性的崩溃(出生于奥本海默)也是如此。为了研究这些现象，使用了一个基于在极紫外(XUV)光谱范围内产生孤立阿秒脉冲的实验实验室。这些化学系统包括对电子叠加、解离过程以及通过电子激发分子的曲线交叉点或锥形交叉点的少飞秒和亚飞秒(阿秒)时间动力学的测量。参与这个以阿秒测量为基础的项目的学生正在获得高科技行业新兴领域的经验。例如，这些包括载波包络相位稳定激光器、光的干涉控制、核心能级光谱学原理、X射线光学程序、电子能谱仪，以及预测电离、轨道占据和排列的速率方程方法。

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.