Multiphoton Ionization and Dissociation: The Phase-Space View

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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.