Phase control of complex autoionizing resonances

近年来，短脉冲极紫外（XUV）光源的发展引起了人们对原子和小分子自电离共振的特别关注。这些共振是由于自电离态而产生的，自电离态通常被视为弱束缚（里德伯）电子和激发离子核的组合。里德伯电子和核心的相互作用导致能量交换，从核心获得能量并释放出弱束缚的电子。当几个这样的状态重叠时，这个简单的图像变得复杂得多。共振的混合导致复杂的光谱，挑战它们的分析和分配。然而，这种复杂的共振也提供了一个独特的机会来研究电子-电子相关性的演变，可能与阿秒时间分辨率。弱束缚里德伯态之间的耦合为用激光场控制关联动力学带来了巨大的潜力。当自电离涉及几个核心状态时，初始超快激发在它们之间产生相干性，并可能导致阳离子核心中的超快空穴迁移。里德伯电子的激光控制使得能够控制离子核中的这种电荷迁移。在这个提议中，我们将研究通过里德伯态控制的概念。我们将冒险进入氮分子的强混合自电离系列的领域，其在离子核心和里德伯态中编码丰富的动力学。我们将采用相干激发的几个重叠的自电离状态的分子与超短XUV脉冲，使用弱NIR可见光激光脉冲作为旋钮来控制激发，并使用时间分辨光电子能谱跟随人口的核心状态。在我们的初步工作中调查的氮分子自电离共振是这个控制概念的优秀候选人。这些共振由两个里德伯态组成，并衰减到两个具有两个不同离子态（氮离子的X和A态）的连续谱。因此，在这个提议中，我们将从理论上发展，并将测试实验控制的两个里德堡态的相对相位。我们将测试两种不同的相位控制方案：通过辅助离散态和通过电离连续。 由于这些共振的混合特性，相位的控制将影响自电离通道的混合，从而将修改离子状态的分支比。通过控制自电离中的分支比，我们的方法能够通过自电离在离子核中形成的电子波包的成形，从而打开了操纵超快电荷迁移的路线。

In recent years, advances in short pulse extreme ultra-violet (XUV) sources have brought special attention to autoionizing resonances in atoms and small molecules. These resonances arise due to autoionizing states, which are often viewed as the combination of a weakly bound (Rydberg) electron and an excited ion core. The interaction of the Rydberg electron and the core leads to energy exchange, taking the energy from the core and liberating the weakly bound electron. This simple picture becomes a lot more complex when several such states overlap. Mixing of resonances results in complex spectra challenging their analysis and assignment. However, such complex resonances also provide a unique opportunity to investigate the evolution of electron-electron correlations, potentially with attosecond time resolution. Couplings between weakly bound Rydberg states carry tremendous potential for control of correlated dynamics with laser fields. When autoionization involves several core states, the initial ultrafast excitation creates a coherence between them and could lead to ultrafast hole migration in the cationic core. Laser control of the Rydberg electrons enables control of this charge migration in the ion core. In this proposal we will investigate this concept of control via Rydberg states. We will venture into the domain of strongly mixed autoionizing series of nitrogen molecules, which encode rich dynamics both in the ionic core and in the Rydberg states. We will employ coherent excitation of several overlapping autoionizing states in molecules with an ultrashort XUV pulse, using a weak NIR-vis laser pulse as a knob to control excitation, and using time-resolved photoelectron spectroscopy to follow populations of the core states. The molecular autoionizing resonances of nitrogen investigated in our preliminary work are excellent candidates for this control concept. These resonances are composed of two Rydberg states and decay towards two continua with two different ionic states (X and A states of the nitrogen ion). Accordingly, in this proposal we will develop theoretically and will test experimentally control of the relative phases of the two Rydberg states. We will test two distinct phase control schemes: through an auxiliary discrete state and through the ionization continuum. Owing to the mixed character of these resonances the control of the phase will influence the mixing of the autoionization channels and thus will modify the branching ratio for the ionic states. By controlling the branching ratio in autoionization our method enables shaping of the electronic wavepacket formed in the ion core by autoionization and thus opens the route to manipulation of ultrafast charge migration.