Structural and multi-dimensional spectroscopy of atoms and molecules on ultrafast time scales using CEP-controlled few-cycle light fields and (continuum-continuum) high-harmonic generation

原子和分子等小量子系统的特征在于它们的空间和能级结构。 测量原子和分子的形状并提取所有量子态的特征能量是物理学、化学和分子生物学中一项古老而持续的奋进。 特别是，空间结构（运动）的时间/动态演化和相关的能级变化（跃迁）是化学反应的核心。 由于电子是化学键的核心成分，这些动力学发生在非常快的时间尺度上的几个飞秒下降到亚飞秒regiments.Here，我们提出了一种实验方法来访问结构和能量分辨的信息在最短的时间尺度上，采用非线性光学过程的高次谐波产生（HHG）的激光，包括一个新的HHG机制，作为探针。根据自己先前的理论工作，传统的高次谐波产生过程可以被修改，以揭示空间静电势结构的时间分辨信息的原子或分子离子被场电离的几个周期的激光脉冲。 在这里，我们将通过观测这些所谓的连续-连续谐波来实验验证并进一步发展这种方法。另一方面，通过载波包络相位（CEP）稳定的几个周期脉冲来产生（甚至是传统的连续束缚）高次谐波，并利用宏观空间自由度进行分析和控制，可以创建一种新型的多维光谱。在传统的二维光谱技术中，诸如人口，更重要的是，电子量子态演化的相干性等属性可以在时间上解决，例如，导致最近发现光合作用中的（量子相干）波动能量传输。 在这里，我们建议将这些技术提升到几个和亚飞秒制度，以瞄准原子和分子中光-物质相互作用过程中的主要几个和多个电子动力学。这些方法的实验组合，以动态结构以及量子态观测，技术上通过四象限时间延迟阶段与宽带宽高谐波软X射线光谱仪串联实现，将创造一种变革性的技术，以提取原子和分子中电子动力学的物理机制，并测试和推进我们目前对多电子过程和强场激光科学的理解。

Small quantum systems such as atoms and molecules are characterized by both their spatial and energy-level structure. It is an old and ongoing endeavor in physics, chemistry, and molecular biology to measure the shape of atoms and molecules and to extract the characteristic energies of all quantum states. In particular, the temporal/dynamical evolution of spatial structure (motion) and the associated energy-level modifications (transitions) is at the heart of chemical reactions. As electrons are the core ingredient of chemical bonding, these dynamics occur on very fast time scales of few femtoseconds down into the sub-femtosecond regime.Here, we propose an experimental approach to access both structural and energy-resolved information on shortest time scales by employing the nonlinear-optical process of high-harmonic generation (HHG) of laser light, including a novel HHG mechanism, as a probe. According to own prior theory work, the traditional high-harmonic generation process can be modified to reveal time-resolved information about the spatial electrostatic-potential structure created by an atomic or molecular ion that was field ionized by a few-cycle laser pulse. We here propose to experimentally demonstrate and further develop this method by observing these so-called continuum-continuum harmonics.On the other hand, performing (even conventional continuum-bound) high-harmonic generation with carrier-envelope phase (CEP)-stable few-cycle pulses, and by making use of the macroscopic spatial degree of freedom for analysis and control, a novel type of multi-dimensional spectroscopy can be created. In traditional two-dimensional spectroscopy techniques, properties such as the population and, more importantly, the coherence of electronic quantum-state evolution can be temporally resolved, leading, for instance, to the recent discovery of (quantum-coherent) wavelike energy transport in photosynthesis. Here, we propose to promote these techniques to the few and sub-femtosecond regime in order to target the primary few- and multi-electron dynamics during light-matter interaction in atoms and molecules.The experimental combination of these approaches to dynamical structural as well as quantum-state observation, technically achieved by a four-quadrant time-delay stage in tandem with a broad-bandwidth high-harmonic soft-x-ray spectrometer, will create a transformative technology to extract physical mechanisms of electron dynamics in atoms and molecules and to test and push forward our current understanding of multi-electron processes and strong-field laser science.