Ionization of multi-electron atomic and molecular systems driven by intense and ultrashort laser pulses

阿秒（10^（-18）秒）是多电子原子和分子完全电离和分裂过程中多电子效应的自然时间尺度。最近在产生超短激光脉冲方面的进展提高了在这个新的时间尺度上研究原子、分子和核物理的可能性，给我们的微观知识和对物质的理解带来了一场革命。原子科学的两个迷人和互补的挑战是确定原子和分子系统中相关多电子动力学（例如分子成像的基本兴趣）的物理机制，并设计探测/控制这些机制的方案。这是本研究的总体目标。操纵电子运动来操纵小分子将为改变复杂生物分子的结构铺平道路，从而影响物理、化学、生物学和材料科学等多个领域。该问题包括探索在强和超短激光脉冲驱动下复杂原子和分子的相互作用。考虑到计算能力的现状，用三维第一性原理技术（即量子力学技术）解决这个问题是一项艰巨的任务。因此，比量子力学快得多的经典/半经典技术将有助于探索驱动复杂原子和分子系统中的相关电子动力学。我最近在氦的驱动双电离的背景下，开发了一种三维经典方法来解决驱动系统的完全分裂。这种技术的优势在于，它比量子力学处理要快得多，而且它解释了库仑奇点——当电子靠近原子中心时，它会受到无限强的力。因此，与先前完全忽略库仑奇点的经典研究相比，这是一个进步。我建议推广这种准经典技术，并开发一种有效而复杂的数值工具来处理复杂驱动的原子和分子系统的完全破碎。使用这种三维准经典技术，我将首先解决由强激光脉冲驱动的三个电子原子中的多电子效应——这是一个尚未探索的问题。其中一个主要目标是探测（时间解析）在原子与一个非常弱的场（单光子吸收）相互作用时，三个电子在碎裂过程中逃逸的主要机制/路径。我将使用圆偏振红外超短激光脉冲作为阿秒时钟，将从观察到的最终碎片光谱获得的信息映射到阿秒相关电子动力学。然后，我将继续探讨在强超短激光脉冲驱动下，具有运动原子核的双活性或双电子双原子分子的双电离中的相关电子动力学。这个问题处于大气科学的前沿，但在理论上还没有得到很好的理解。使用不同强度的脉冲，我将能够探索不同的电离机制，对于每个机制，探索控制两个电子逸出的不同机制，两个原子中心对双重电离的影响，以及导致不同最终产物的过程的相互作用。我们的愿景是将这些研究推广到解决具有移动原子核的驱动三原子分子——一个尚未探索的问题——并研究破裂几何形状及其对初始分子状态的依赖。最后，结合我在探测单光子过程和强驱动分子的多电子效应方面的专业知识，我将利用超短激光脉冲组合解决驱动多中心分子破裂过程中的时间分辨和控制电子运动问题。

Attoseconds (10^(-18) sec) are the natural time-scale for multi-electron effects during complete ionization and break-up of multi-electron atoms and molecules. The recent advances in generating ultrashort laser pulses raise the possibility to investigate atomic, molecular, and nuclear physics at this new time-scale, bringing a revolution in our microscopic knowledge and understanding of matter. Two fascinating and complementary challenges of Attoscience are to identify the physical mechanisms underlying the correlated multi-electron dynamics--of fundamental interest to, for instance, molecular imaging--in atomic and molecular systems and to devise schemes to probe/control these mechanisms. This is the overall aim of the proposed research. Steering the electronic motion for manipulating small molecules will pave the way for modifying the structure of complex biomolecules, thus impacting such diverse fields as physics, chemistry, biology and material science. The problem consists of exploring the interaction of complex atoms and molecules driven by intense and ultrashort laser pulses. Given the state of the art in computational capabilities, solving this problem with three-dimensional (3-d) first-principle techniques, namely, quantum mechanical ones, is an immense task. Thus, classical/semiclassical techniques, which are much faster than quantum mechanical ones, will be instrumental in exploring the correlated electron dynamics in driven complex atomic and molecular systems. I recently developed, in the context of the driven double ionization of Helium, a 3-d classical method that addresses the full fragmentation of driven systems. The advantage of this technique is that it is much faster than quantum mechanical treatments and it accounts for the Coulomb singularity--the infinitely strong force an electron experiences when it is close to the atomic center. It is thus a step forward compared to previous classical studies which ignore the Coulomb singularity altogether. I propose to generalize this quasiclassical technique, and develop an efficient and sophisticated numerical tool for the treatmentof the full fragmentation of complex driven atomic and molecular systems.Using this 3-d quasiclassical technique, I will first address multi-electron effects in three electron atoms driven by strong laser pulses--a problem vastly unexplored. One of the main goals is to probe (time-resolve) the main mechanisms/paths the three electrons follow to escape during the fragmentation process when the atom is interacting with a very weak field (single photon absorption). I will do so using a circularly polarized infrared ultrashort laser pulse as an attosecond clock to map the information obtained from the observed spectra of the final fragments to the attosecond correlated electron dynamics. I will then proceed to explore the correlated electron dynamics in the double ionization of two- active or two-electron diatomic molecules with moving nuclei when driven by intense ultrashort laser pulses. This problem is at the forefront of Attoscience and is far from being theoretically well understood. Using pulses of different intensity I will be able to explore different ionization regimes and for each regime explore the different mechanisms that govern the two electron escape, the effect of the two atomic centers on the double ionization, and the interplay of processes that result in different final products. The vision is to generalize these studies to tackle driven triatomic molecules with moving nuclei--an unexplored problem--and study the break-up geometries and their dependence on the initial molecular state. Finally, combining my expertise on probing single photon processes and on multi-electron effects of strongly driven molecules, I will address time-resolving and controlling the electronic motion during the break-up of driven multi-center molecules using combinations of ultrashort laser pulses.