CADAM: Capturing Attosecond Dynamics in Atoms and Molecules

在原子、分子或生物系统中，所有结构变化都会改变实体的性质（形式、颜色、与其他实体反应的能力等）。这些变化是由于电子和核动力学称为电荷迁移（电子和/或质子在实体内的重排）。然而，电荷迁移非常快，可以在1/1000 000 000 000 000秒内发生，这意味着从几阿秒（1e-18秒）到几飞秒（1e-15秒）。举个例子，在卢瑟福的氢原子模型，也就是众所周知的“行星”模型中，一个电子绕着一个质子（第一轨道）运动。电子绕质子一周所需的时间是150秒。特别令人兴奋的是，能够将这种超快的动态制作成“电影”，这是现有设备无法做到的。实际上，我的兴趣不仅在于观察这些结构变化的最初瞬间，而且在于控制它们，从而更深入地理解化学反应或生物现象是如何发生的。如果实现这种阿秒级的信息，就有可能实现非常高速的信息传输，为什么不研究如何将信息人工编码（分子电子学）或在生物样本中呈现（癌症痕迹），这是一种生物计算？这项研究将产生一种新型的物理学，它将弥合许多科学之间的差距。该研究领域的技术挑战是在激光开发方面的领先国际努力，这将对工业（电子，通信），医学技术（磁共振成像，质子治疗，药理学）的技术应用产生巨大影响。因此，我开展了一项基于工具来观察和控制原子内和分子内电子和原子核运动的研究。为了在任何化学或生物反应的起源处捕捉这种动态，人们必须捕捉系统进化的快照，就像照相机一样。不幸的是，没有这样的探测器，但有可能找到一个可观察的过程，它可以受到这些变化的影响，因此将携带这些变化的指纹。理想的候选者是光，因为光子的发射对任何变化都高度敏感，这是一个快速的过程，可以通过观察光谱（频率相当于它的颜色）来观察。我选择的过程是高次谐波产生（HHG），发生在10阿秒到几fsec（适当的时间窗口）。当强而短的激光脉冲与原子或分子相互作用时，它就会发生。在这种相互作用中，一个电子被电离（从核心中提取出来），在回到核心之前遵循一定的轨迹，在那里它可以被重新捕获，就像一个返回的回旋镖。电子在其运动过程中获得的多余动能将被系统（最终的原子或分子）消耗，释放出一个新的光子，该光子的频率（颜色）将是基本光子（激光光子）的奇谐波。这些谐波光子可以被精确地测量，因此如果在电子运动过程中磁心发生变化，所发射光子的特性将被改变。我一直致力于高次谐波的研究，特别是在这个过程中对电子轨迹的理解。我通过实验证明，电离的电子不仅可以遵循一个轨迹，而且可以遵循多个轨迹，从而产生了我的研究技术，称为量子路径干涉，首先在原子中得到了证明。我将在不同的条件下使用这种技术来提取分子在阿秒时间尺度内的电荷迁移信息。

In atoms, molecules or biological systems, all structural changes will modify the properties of the entity (form, colour, capacity to react with other entities etc ...). These changes are due to electronic and nuclear dynamics known as charge migrations (rearrangement of electrons and/or protons within the entity). However charge migrations are very fast and can occurs within 1/1000 000 000 000 000 second meaning from few attosecond (1e-18 sec) to few femtosecond (1e-15 sec). As an example in the Rutherford model of the hydrogen atom, known as the "planetary" model, an electron is moving around a proton (first orbital). The duration the electron takes to complete period around the proton is 150 asec. What is particularly exciting is to be able to make "a movie" of this ultra-fast dynamic that no existing device is capable to follow. My interests are actually not only to observe the first instants of these structural changes but also to control them to go deeper in the understanding of how chemical reactions or biological phenomena take place. If such attosecond information is achieved it will be possible to approach very high-speed information transfer and why not studying how information can be artificially encoded (molecular electronics) or present (traces of cancers) in biological sample, a kind of bio computing?This research will give birth to a new type of Physics that will bridge the gap between many sciences. The technical challenges under this research area are leading international efforts in laser development that will have a huge impact on technological applications also in industry (electronic, communication), medicine technologies (Magnetic Resonance Imaging, proton therapy, pharmacology).Therefore I developed a research based on tools to observe and control the intra- atomic and intra-molecular electrons and nuclei motions. To capture this dynamics at the origin of any chemical or biological reactions, one has to capture snapshots of the system evolving, exactly as a camera will do. Unfortunately there is no such detector, but what is possible is to find a process observable, that can be affected by these changes and so that will carry the fingerprint of these changes. The ideal candidate for this is light, because emission of photons is highly sensitive to any changes, it is a fast process and it can be observable by looking at spectra (frequency equivalent to its colour). The process I choose is high-order harmonic generation (HHG) that occurs within 10's attosec to few fsec (appropriate time window). It occurs while an intense and short laser pulse interacts with an atom or a molecule. During this interaction, an electron is ionised (extract from the core), and follow a certain trajectory before coming back to the core where it can be recaptured, exactly as a returning boomerang. The excess kinetic energy the electron has acquired during its travel will be spent by the system (final atom or molecule) emitting a new photon which frequency (colour) will be an odd harmonic of the fundamental photon (the laser photon). These harmonic photons can be measured accurately so if a change in the core occurs during the electron travel, the characteristic of the photons emitted will be modified. I have been working in the study of high order harmonic and in particular in the understanding of electron trajectories during the process. I demonstrated experimentally that the ionised electron can not only follow one trajectory but many, giving rise to my technique of investigation called Quantum-Path Interferences first demonstrated in atoms. I will use this technique under different conditions to extract the information on charge migration in molecules within the attosecond timescale.