Phase control of complex autoionizing resonances

近年来，短脉冲极紫外线（XUV）光源的进展引起了人们对原子和小分子自电离共振的特别关注。这些共振是由自电离状态引起的，通常被认为是弱束缚（里德伯）电子和激发离子核的结合。里德伯电子和核的相互作用导致能量交换，从核中获取能量并释放弱束缚电子。当几个这样的状态重叠时，这个简单的图景变得复杂得多。共振的混合导致复杂的光谱，对它们的分析和分配提出了挑战。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-电子相关的演变，可能具有阿秒的时间分辨率。弱束缚里德伯态之间的耦合对于控制激光场的相关动力学具有巨大的潜力。当自电离涉及多个核态时，初始超快激发会在核态之间产生相干性，从而导致阳离子核中的超快空穴迁移。激光控制里德堡电子可以控制离子核中的电荷迁移。在本提案中，我们将通过里德伯格态来研究这种控制概念。我们将冒险进入强混合自电离系列氮分子的领域，它们在离子核和里德伯态中都编码了丰富的动力学。我们将使用超短XUV脉冲相干激发分子中几个重叠的自电离态，使用弱NIR-vis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来跟踪核心态的居群。我们初步研究的氮分子自电离共振是这种控制概念的优秀候选者。这些共振由两个里德伯态组成，并衰变成两个具有两种不同离子态（氮离子的X态和A态）的连续体。因此，在这个建议中，我们将从理论上发展和实验上测试两个里德伯态相对相的控制。我们将测试两种不同的相位控制方案：通过辅助离散状态和通过电离连续体。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，从而改变离子态的分支比。通过控制自电离中的分支比，我们的方法能够塑造由自电离在离子核中形成的电子波包，从而开辟了操纵超快电荷迁移的途径。

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.