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

在过去的几年里，定制强激光脉冲的设备一直在彻底改变原子和分子阿秒强场光谱仪。它们的本质被广为人知和广泛使用的三步模型所捕捉到。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再碰撞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工作中，我们检验了一个中心假设，即对于相同比例的电离事件，无论分子相对于激光偏振的取向如何，都会发生再碰撞。我们的实验基于激光驱动的电子在单个分子中重新散射到不同的强电离连续体中的分离。我们最近的结果确实对分子的激光诱导电子衍射(LID)具有重要的意义，这是一种新兴的技术，在这种技术中，分子通过自己的一个电子自成像。LISE有望成为传统电子束衍射的时间分辨变体，这是获得分子结构信息的一种强大方法。在标准的LIE分析中，假定返回波包振幅的关键分子框架依赖于强场电离几率的分子框架依赖关系。这一假设与我们最近的实验和理论发现形成了鲜明的对比，即电离电子的分子框架依赖部分发生再碰撞。在这里，我们建议定量地探索LID分子结构确定对返回概率的分子框架依赖的敏感性。为了实现这一目标，我们想要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再散射几率的分子框架依赖关系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，我们还计划通过操纵强激光场来控制传输中的连续电子的连续轨道。这将使我们能够引导电子波包的不同部分重新碰撞，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及其离子的非弹性重散射，以更好地了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重散射至关重要，这是自信地利用强大的分子动力学和化学的时间分辨探针的先决条件。

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.