Theoretical Atomic Attosecond Spectroscopy: Monitor and Control of Electron Correlation in Real Time

该项目旨在开发新的非标准计算工具，用于表示多电子原子系统与超短“阿秒”光脉冲的相互作用。这些超短脉冲就像高速照相机一样，能够成像电子在原子和/或分子中的运动。因此，它们提供了一幅与电子运动相关的复杂动力学的独特图景，并可能提供一个机会来控制电离和其他碎裂过程的结果，即使在复杂的、高度相关的材料中也是如此。在如此短的时间尺度上表示电子运动的严峻计算挑战来自测不准原理，该原理表明将需要准确地描述跨越广泛能量范围的原子和/或分子状态，包括其中两个或更多电子同时被激发的高能态。因此，该项目应阐明多重激发态在阿秒辐射脉冲吸收引起的碎裂过程中的作用。超短激光脉冲在原子中触发的动力学状态的理论描述是具有挑战性的，因为它需要在广泛的能量范围内表示几个电子态，这些电子态通过发射光电子而衰变。被释放到连续体的电子与它们留下的母离子以及阿秒泵浦-探测实验中常用的修整激光脉冲强烈相互作用。为了解决这些困难，这个项目将结合对一般多电子原子在任意外场存在下的含时薛定谔方程的并行模拟技术，以及用多组态Hartree Fock B样条紧耦合方法表示的最先进的数值方法来计算静止束束态、多通道单电离散射原子函数和Siegert态。该项目开发的数值工具将用于研究稀有气体原子中驱动多电子阿秒动力学的未探索方面，特别侧重于自电离态的作用，自电离态是建立光碎裂过程相干控制方案的持久参照的最佳近似值。特别是，该项目将通过光学和光电子阿秒干涉泵浦-探测方案探索瞬时束缚波包的创建、成像和定制。该项目将研究如何使用瞬变相干来控制光电离事件中的分支比、角分布和剩余离子相干性。激光驱动的自电离态的性质，如它们的交流-斯塔克移动，它们的隧穿速率，以及被修饰的原子在极端紫外线(XUV)范围内的电极化率，将被绘制成图表。我们将研究电子关联对这些性质的影响，这些信息将被用来帮助控制系统内的布居转移以及穿过目标的XUV光的光谱和形状。

This project is aimed at the development of new, non-standard computational tools for representing the interaction of poly-electronic atomic systems with ultra-short "attosecond" light pulses. These ultra-short pulses act like high speed cameras capable of imaging the motion of electrons within atoms and/or molecules. They accordingly provide a unique picture of the complex dynamics associated with electron motion, and may also provide an opportunity to control the outcome of ionization and other fragmentation processes, even within complex, highly-correlated materials. The severe computational challenge of representing the motion of electrons on such short time scales derives from the uncertainty principle, which indicates that atomic and/or molecular states spanning a broad energy range will need to be accurately described, including high energy states in which two or more electrons are simultaneously excited. The project should accordingly shed light on the role of multiply-excited states in fragmentation processes induced by the absorption of attosecond radiation pulses. The theoretical description of the dynamical regimes triggered in atoms by ultrashort laser pulses is challenging because it entails the representation of several electronic states, across a wide energy range, that decay by emitting photoelectrons. The electrons liberated to the continuum interact strongly with the parent ion they leave behind, as well as with the dressing laser pulses commonly employed in attosecond pump-probe experiments. To tackle these difficulties, this project will merge parallel simulation techniques for the time-dependent Schrodinger equation of general poly-electronic atoms in the presence of arbitrary external fields, with state-of-the-art numerical methods to compute stationary bound states, multichannel single-ionization scattering atomic functions, and Siegert states, represented in terms of a multi-configuration Hartree Fock B-spline close-coupling approach. The numerical tools developed in the project will be applied to study unexplored aspects of driven multi-electron attosecond dynamics in rare gas atoms, with a special focus on the role of autoionizing states, which constitute the best approximation of a persistent reference onto which building coherent-control schemes for photo-fragmentation processes. In particular, the project will explore the creation, imaging and tailoring of transiently bound wavepackets, by means of both optical and photoelectron attosecond interferometric pump-probe schemes. The project will study how transient coherences can be used to control branching ratios, angular distributions, and residual-ion coherence in photoionization events. Properties of laser-driven autoionizing states, such as their ac-Stark shift, their tunnelling rate, and the electric susceptibility of dressed atoms in the extreme ultraviolet (XUV) range, will be charted. The affect of electron correlation on these properties will be studied, and this information will be used to help control population transfer within the system as well as the spectrum and shape of the XUV light transmitted through the target.