Application of XUV and Soft-x-ray Attosecond Spectroscopies to Quantify Vibronic Couplings and Charge Dynamics

我们日常生活中许多现象背后的主要量子过程是电子的光驱动运动。这方面的重要例子包括光合作用、视觉、阳光下维生素D的合成、紫外线对DNA的损伤等等。作为更好地理解这种现象的第一步，重要的是用光脉冲研究和利用原子和简单分子内部的电子运动。然而，电子的速度非常快，可以在一个阿秒的时间尺度上移动——十亿分之一秒的十亿分之一！要想以如此令人眩晕的速度捕捉量子领域中发生的事情，人们需要使用精密的相机和极快的闪光灯或频闪灯。PI的团队采用了先进的技术，如带电粒子速度成像探测器，它起到了相机胶片的作用，以及超快的激光脉冲，起到了闪光灯的作用。该研究计划将调查在光激发后电子电荷如何分布，以及分子内原子位置的变化如何影响这一过程。从事这个项目的研究生和本科生将培养一套重要的科学技能，并将被授权产生新的想法和设计应用他们的研究。随着他们进入大学、国家实验室和科技公司的职业生涯的下一个阶段，这种影响将成倍增加，从而促进社会的科学创新和生产力。阿秒极紫外和软x射线光谱技术为电子动力学的基础实时研究提供了非常强大的工具。在提议的工作中，PI和研究生将采用这些方法进行相干电子波包运动的时间分辨研究。具体来说，他们将研究XUV在原子和分子中诱导的里德伯，离子和多电子激发。为了量化由于核运动而混合电子态的振动耦合，研究小组将在小分子的锥形交叉点附近进行泵浦探针测量。他们还将致力于进行元素特异性瞬态吸收研究，以监测光电离分子中电荷的相干演化。这里获得的结果将指导理论方法的发展，可以准确地模拟光-物质相互作用，以及电子和原子核的耦合和相关演化。复杂系统中电荷动力学的时空映射将有助于建立阿秒科学作为一种通用的光谱技术。这些目标将在培养阿秒科学、激光技术、光学和x射线光谱学等前沿领域的研究生和本科生的同时实现。PI还将强调少数民族和代表性不足群体学生的参与。每年的外展活动将用于参与和教育社区关于物理研究的重要性和影响。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

The primary quantum process behind many phenomena in our daily lives is the light-driven motion of electrons. Important examples of this include photosynthesis, vision, vitamin D synthesis from sunlight, DNA damage by UV light, and more. As a first step towards developing a better understanding of such phenomena, it is important investigate and harness the electronic motions inside atoms and simple molecules with light pulses. However, the electrons are extremely fast, and can move on the timescale of an attosecond – a billionth of a billionth of a second! To capture the images of what transpires in the quantum realm at such dizzying speeds, one needs to use a sophisticated camera alongside an extremely fast flash or strobe light. The PI’s team employs advanced technologies such as a charged particle velocity imaging detector, which serves the purpose of a camera film, and ultrafast laser pulses that play the role of a strobe light. The proposed research project will investigate how electronic charge gets distributed after excitation by light, and how the changes in atomic positions within a molecule impact this process. Graduate and undergraduate students working on this this project will develop an important scientific skillset and will be empowered to generate new ideas and devise applications of their research. This impact will multiply as they move to the next stage of their careers in universities, national labs, and tech companies, thus fostering scientific innovation and productivity in the society.Attosecond extreme ultraviolet and soft-x-ray spectroscopy techniques form a very powerful toolkit for fundamental, real-time investigations of electron dynamics. In the proposed work, the PI and graduate students will employ these approaches for time-resolved study of coherent electronic wavepacket motion. Specifically, they will investigate XUV induced Rydberg, ionic, and many-electron excitations in atoms and molecules. To quantify the vibronic couplings that mix electronic states due to nuclear motion, the research team will conduct pump-probe measurements near conical intersections in small molecules. They will also aim to perform elementally specific transient absorption studies to monitor the coherent evolution of charge in photoionized molecules. Results obtained here will guide the development of theoretical methods that can accurately model the light-matter interaction, and the coupled and correlated evolution of electron and nuclei. The spatio-temporal mapping of charge dynamics in complex systems will serve to establish attosecond science as a versatile spectroscopy technique. These objectives will be achieved while training the graduate and undergraduate students in the frontier fields of attosecond science, laser technologies, and optical and x-ray spectroscopies. The PI will also place an emphasis on the participation of students from minority and underrepresented groups. Annual outreach events will be used to engage and educate the community about the importance and impact of physics research.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.