Multiphoton Ionization and Dissociation: The Phase-Space View

实时成像生物分子的内部运动可能会导致对生物系统和过程的理解的重要改进。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。激光物理界正在努力开发这些来源，方法是利用超快、超强激光脉冲将电子从分子中抛出时发出的辐射，这种脉冲首先将电子加速离开分子，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不会被捕捉到被拉回，而是在强大的激光场中远离它们的母体分子，从而丢失。然而，那些确实找到了返回其母分子的方法的分子携带着它们从激光中吸收的能量，因此能量足够用作物理学家寻找的光源。因此，预测哪些电离电子将返回它们的母体分子，哪些将不会有太大意义。这个项目将专注于开发改进的数学模型来促进这种预测，从而建立指向更明亮的光源和改进的成像能力的条件。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将导致“重新碰撞”的条件(即上文讨论的罕见但重要的返回过程)。以前的工作已经确定，强场物理的一些关键的量子方面可以被经典力学理解：事实上，再碰撞物理的标准工作模型，即所谓的“三步走”情景，包括“电离/在激光场中旅行/返回核心”，从经典等离子体的角度来看待这一情景的关键组成部分。非线性动力学非常适合于揭示机制，可以用来利用这一最新的见解。通过关注轨迹集合而不是单个轨迹的集体行为，现在已经解释了再碰撞现象中的相当多的悖论，这些悖论由于没有可行的计算方法来研究而一直没有解决。在接下来的几年里，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机械师合作，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.