Ionization Channel-Resolved Molecular Orbital Imprint in Laser-Driven Electron Rescattering

在过去的几年里，裁剪强激光脉冲的设备已经彻底改变了原子和分子的阿秒强场光谱。它们的本质被著名的、广泛使用的三步模型所捕捉。这三个步骤包括激光驱动的隧道电离、电子在连续介质中的传播以及它在回忆时与离子核的相互作用。所有这些步骤在激光周期的一小部分内连续发生。在我们最近关于激光驱动的电子再散射的研究中，我们检验了一个中心假设，即对于相同比例的电离事件，无论分子取向与激光极化有关，都会发生回忆。我们的实验基于激光驱动的电子再散射在单个分子中分离成不同的强电离连续体。我们最近的研究结果可能对分子的激光诱导电子衍射（LIED）有重要的影响，这是一种新兴的技术，分子通过它们自己的一个电子自我成像。它有望成为传统电子束衍射的时间分辨变体，是获得分子结构信息的有力方法。在标准的红外光谱分析中，假定返回波包振幅的关键分子框架依赖关系简单地由强场电离概率的分子框架依赖关系给出。这一假设与我们最近的实验和理论发现形成鲜明对比，即电离电子的分子框架依赖部分会发生回忆。在这里，我们提出了定量探索的灵敏度，确定分子结构的分子框架依赖于返回概率。为了实现这一目标，我们希望分别对两个分子强场电离通道进行分子结构分析。此外，我们的目标是将我们最近对电子重散射概率的分子框架依赖性的部分重建扩展到完全重建。这将分别访问每个电离通道的极角和方位角。此外，我们计划通过操纵强激光场来控制传播的连续电子的连续轨迹。这将使我们能够引导电子波包的不同部分重新收集，从而表征其结构，这取决于分子轨道及其对强激光场的响应。最后，我们计划研究激光驱动的连续电子与其离子的非弹性重散射，以更好地理解它们之间的相互作用。这里提出的研究对于详细理解激光诱导的电子再散射至关重要，这是自信地利用激光诱导电子再散射成为强大的时间分辨分子动力学和化学探针的先决条件。

During the last few years, the facility in tailoring intense laser pulses has been revolutionizing the atomic and molecular attosecond strong-field spectroscopies. Their essence is captured by the well-known and widely-used three-step model. The three steps consist of laser-driven tunnel ionization, propagation of the electron in the continuum and its interaction with the ion core upon recollision. All of these steps occur consecutively within a fraction of a laser cycle. In our recent work on laser-driven electron rescattering we have examined the central assumption that recollision occurs for the same fraction of ionization events, regardless of the molecular orientation with respect to the laser polarization. We base our experiments on the separation of laser-driven electron rescattering into different strong-ionization continua in a single molecule.Our recent results do potentially have important consequences for Laser-Induced Electron Diffraction (LIED) of molecules, an emerging technique in which molecules are self-imaged by one of their own electrons. LIED promises to become a time-resolved variant of conventional diffraction with electron beams, a powerful method to obtain structural information on molecules. In standard LIED analyses it is assumed that the crucial molecular frame dependence of the amplitude of the returning wavepacket is simply given by the molecular frame dependence of the strong-field ionization probability. This assumption is in marked contrast with our recent experimental and theoretical finding that recollision occurs for a molecular-frame dependent fraction of the ionized electrons.Here we propose to quantitatively explore the sensitivity of the LIED molecular structure determination to the molecular-frame dependence of the return probability. To achieve this objective, we want to perform a molecular structure analysis separately for two molecular strong-field ionization channels. Moreover, we aim to extend our recent partial reconstruction of the molecular-frame dependence of the electron rescattering probability to a full reconstruction. This will access both the polar angle and the azimuthal angle separately for each ionization channel. Furthermore, we plan to control the continuum trajectory of the propagating continuum electron by manipulating the strong laser field. This would allow us to steer different parts of the electron wavepacket to recollision, thus characterizing its structure which depends on the molecular orbitals and their response to the strong laser field. Finally, we plan study the inelastic rescattering of the laser-driven continuum electron with its ion to better understand their interaction.The research proposed here is crucial for understanding laser-induced electron rescattering in detail, a prerequisite for confidently harnessing LIED into a powerful time-resolved probe of molecular dynamics and chemistry.