Multiphoton Ionization and Dissociation: The Phase-Space View

在真实的时间内对生物分子的内部运动进行成像，可以大大提高对生物系统和过程的理解。实现这一梦想将需要前所未有的新成像工具，这些工具依赖于先进的光源。 激光物理学界正在努力开发这些光源，方法是利用超快、超强的激光脉冲将电子从分子中射出时发出的辐射，激光脉冲首先加速电子远离分子，然后将电子抛回分子中产生辐射脉冲。 问题是，大多数被移除的电子并没有被捕获并被拉回，而是在强激光场中远离它们的母体分子漂移，从而丢失。然而，那些确实找到回到母体分子的方式的分子携带着它们从激光中吸收的能量，因此具有足够的能量作为物理学家所追求的光源。因此，预测哪些电离电子将返回到它们的母体分子，哪些将不重要。 该项目将致力于开发改进的数学模型以促进这一预测，从而建立指向更亮光源和改进成像能力的条件。令人惊讶的是，过去六年的工作表明，分子场系统的共振决定了导致“再碰撞”（即上文讨论的罕见但重要的返回过程）的条件。先前的工作已经确定，强场物理学的一些关键量子方面可以通过经典力学来理解：事实上，电离物理学的标准工作模型，即所谓的“三步”场景，由“电离/在激光场中旅行/返回核心”组成，从经典等离子体的角度看待这个场景的关键组成部分。非线性动力学，这是非常适合于发现机制，可以用来利用这一最新的见解。通过关注轨迹集合的集体行为，而不是单个轨迹，现在已经解释了由于没有可行的计算方法来研究它们而一直未解决的许多悖论。在今后几年中，将对这些过程的数学模型进行必要的改进。在这个过程中，将进入未知的数学领域，需要与数学家和天体力学家合作，以进一步推进这些革命性新光源的发展目标。

Imaging the internal motions of biomolecules in real time could lead to important improvements in understanding of biological systems and processes. Realizing this dream will require unprecedented new imaging tools that rely on advanced light sources. The laser physics community is hard at work trying to develop these sources by capitalizing on the radiation that is emitted when an electron is ejected from a molecule by an ultra-fast, ultra-strong laser pulse that first accelerates the electron away from the molecule but then hurls the electron back into the molecule to generate a pulse of radiation. The hitch is that most of the electrons that are removed are not caught to be pulled back but drift far from their parent molecules in a strong laser field and are thereby lost. However, those that do find their way back to their parent molecule carry with them the energy they absorbed from the laser, and are therefore energetic enough to serve as the light sources physicists are after. Therefore, predicting which ionized electrons will return to their parent molecule and which will not matters greatly. This project will focus on developing improved mathematical models to facilitate this prediction, thereby establishing conditions that point to brighter light sources and improved imaging capabilities.Work of the last six years shows, surprisingly, that resonances of the molecule-field system, determine the conditions that will lead to a "re-collision" (that is, the rare, but important return processes discussed above). Prior work had established that some critical quantum aspects of strong-field physics could be understood by classical mechanics: Indeed, the standard working model of recollision physics, the so-called "three-step" scenario consisting of "ionization/travel in the laser field/return to the core", views key components of this scenario from a classical plasma perspective. Nonlinear dynamics, which is ideally suited to uncovering mechanisms, can be used to exploit this recent insight. By focusing on the collective behavior of ensembles of trajectories rather than individual trajectories, quite a few paradoxes in recollision phenomena which had remained unresolved because no feasible computational method was available to investigate them, have now been explained. Over the next few years, needed improvements of the mathematical models of these processes will be pursued. In the process, uncharted mathematical territory will be entered, requiring collaborations with mathematicians and celestial mechanicians to further advance the goal of development of these revolutionary new light sources.