Attosecond Photoemission Dynamics: Novel AB Initio Methods for Atomic and Molecular Ex-situ Spectrscopies

在基本层面上，原子由带负电荷的粒子——电子——组成，它们围绕着一个巨大的带正电荷的原子核飞行。利用超短激光脉冲，电子的快照可以以阿秒的时间分辨率拍摄（一阿秒是十亿分之一秒的十亿分之一），这是电子运动的自然时间尺度。然而，为了控制原子如何随时间演化，预测它们的快速动力学也是必不可少的。这是一项困难的任务，因为电子在绕原子核运动时试图避开彼此。此外，电子偶尔会发生碰撞，导致舞蹈的编排发生变化。在过去的三年里，这个研究小组开发了数值工具，可以预测这种复杂的动力学在外部光脉冲的影响下如何展开。本项目将在理论工具箱中增加描述电子动力学三个重要方面所必需的部分；它们的自旋与轨道运动的相互作用，它们与圆偏振光的相互作用，在分子电子的情况下，它们与两个或更多核中心的相互作用。这些新工具将有助于巩固美国在超快原子和分子国际社会中的地位，并为参与这项研究的学生提供独特的计算技能。阿秒脉冲为原子和分子中超过电离阈值的电子激发提供了时间分辨研究的途径。这些研究依赖于更加复杂的理论模型。目前，在静电近似中，有可能描述像氖和氩这样复杂的系统的电离。然而，对第一周期以外的原子的精确处理需要结合它们的自旋轨道相互作用。由于实验的不断进步，现在可以随意改变阿秒光脉冲的偏振，并且可以从定向分子目标中检测角度分辨的光电子能谱。该项目将包括自旋轨道效应和在时间分辨原子电离描述中与任意极化脉冲的相互作用，并将现有的分子散射代码扩展到有限脉冲多光子电离机制。包含相对论相互作用对于量化由于自旋轨道相互作用和电子相关性之间的相互作用而引起的电离延迟是必不可少的。对任意极化超短脉冲电离的研究将为非轴对称光发射开辟道路。新的分子密码将为阿秒干涉光谱提供更严格的基础。该项目旨在解决原子阿秒实验中持续存在的差异，这些差异是由于氩和氪等重原子的价层和内价层中不可忽略的自旋轨道分裂造成的。它将探索具有圆极化脉冲的新型泵浦方案，这是直接测量光发射中的共振延迟和手性系统电离的二色性的关键。该项目还将通过校外培训课程，促进当地高中学生参加美国物理奥林匹克竞赛，从而促进佛罗里达州STEM的卓越发展。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。

At a fundamental level, atoms consists of negatively-charge particles, the electrons, flying around a massive positively-charged nucleus. Using ultrashort laser pulses, snapshots of electrons can be taken with attosecond time resolution (one attosecond is a billionth of a billionth of a second), which is the natural timescale of electronic motion. To control how atoms evolve in time, however, it is also essential to be able to predict their fast dynamics. This is a difficult task because electrons try to avoid each other in their motion around the nucleus. Furthermore, electrons occasionally do collide, causing the choreography of the dance to change. During the last three years, this research group has developed numerical tools that can predict how this complex dynamics unfolds under the influence of external light pulses. The present project will add to the theoretical toolbox the pieces necessary to describe three important aspects of electron dynamics; the interaction of their spin with their orbital motion, their interaction with circularly polarized light, and, in the case of molecular electrons, their interaction with two or more nuclear centers. These new tools will contribute to consolidate the U.S. presence in the ultrafast atomic and molecular international community, and to equip the students involved in this research with unique computational skills.Attosecond pulses have given access to the time-resolved study of electronic excitations in atoms and molecules above their ionization threshold. Such studies rely on ever more sophisticated theoretical models. Currently, it is possible to describe, within the electrostatic approximation, the ionization of systems as complex as neon and argon. Yet, the accurate treatment of atoms beyond the first period requires incorporation of their spin-orbit interaction. Thanks to constant experimental advances, the polarization of attosecond light pulses can now be changed at will, and it is possible to detect angularly resolved photoelectron spectra from oriented molecular targets. This project will include spin-orbit effects and the interaction with arbitrarily polarized pulses in the time-resolved description of atomic ionization, and it will extend existing molecular scattering codes to finite-pulse multi-photon ionization regimes. The inclusion of relativistic interactions will be essential to quantify the ionization delay due to the interplay between spin-orbit interaction and electron correlations. The study of ionization with arbitrarily polarized ultrashort pulses will open the way to non-axially symmetric photoemission. The new molecular-codes will be a more rigorous basis for attosecond interferometric spectroscopies. This project aims at solving persistent discrepancies in atomic attosecond experiments that are due to the non-negligible spin-orbit splitting in the valence and inner-valence shells of atoms as heavy as argon and krypton. It will explore new pump-prope schemes with circularly-polarized pulses, which hold the keys to the direct measurement of resonant retardation in photoemission and to the dichroism in the ionization of chiral systems. This project will also foster STEM excellence in Florida by promoting the participation of students from local high schools to the USA Physics Olympiads through off-campus training sessions.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.