Strong Field and Ultrafast Atomic and Molecular Processes

这个项目的重点是从理论上理解强相干辐射与原子和分子的相互作用，并研究使用超快(阿秒尺度)激光或电子脉冲来泵浦或探测原子和分子中的电子过程。这种过程很难在理论上处理，因为与强激光场以及与原子和分子势的电子相互作用通常必须以非微扰方式描述；此外，与短激光或电子脉冲的相互作用必须以依赖时间的方式描述。为了支持这些研究，我们开发了一些新的理论方法。研究包括使用阿秒尺度的电子脉冲作为原子和分子中电子运动的时间和空间探测器；研究激光强度引起的电离电子产额与所谓的“ATI平台”相对应的电子能量的来源；发展新的封闭形式的负离子高次谐波产生幅度和速率的解析公式，将这些结果推广到中性原子，并将这些结果应用于寻找提高高次谐波产额的方法；以及研究短脉冲激光在高次谐波产生中的双电子效应。参与该项目的研究生和博士后研究人员将接受广泛的理论原子物理教育，在科学交流的所有方面都有第一手经验，并在一所大型AAU Land Grant大学教授本科生。项目成果不仅发表在领先的物理学期刊上，并在国内和国际会议上展示，而且还定期提炼并与其他人的相关工作结合在由国际和平研究所和合作者撰写的评论文章中。过去参与该项目的所有研究生和博士后研究人员都受到了各种其他雇主的追捧，包括技术公司、医学研究人员和其他领先的AMO理论团体。这个项目支持的基础研究广泛地有助于我们理解在原子尺度上控制物质的方法。我们在提高高次谐波强度方面的工作有朝一日可能会产生相干X射线源，从而为可视化生物结构和纳米材料结构提供一种新的手段。我们对阿秒电子脉冲的研究可能会导致在时间和空间上解决电子运动的方法。科协2006年在卡夫利理论物理研究所共同举办的阿秒科学讲习班有助于加强这一新兴学科研究的基础设施。2008年，P.I.S参与编辑了《新物理杂志》关于阿秒科学的一期特刊，这证明了他对研究界的持续服务。

This project focuses on understanding theoretically the interaction of intense coherent radiation with atoms and molecules and on investigating the use of ultrafast (attosecond scale) laser or electron pulses to pump or probe electronic processes in atoms and molecules. Such processes are difficult to treat theoretically because electronic interactions with both intense laser fields and with atomic and molecular potentials must in general be described non-perturbatively; also, interactions with short laser or electron pulses must be described time-dependently. In support of these investigations we have developed a number of new theoretical approaches. Investigations include using attosecond scale electron pulses as both temporal and spatial probes of electronic motion in both atoms and molecules; investigating the origin of laser-intensity-induced enhancements of ionized electron yields for electron energies corresponding to the so-called "ATI plateau"; developing novel closed form analytic formulas for high order harmonic generation amplitudes and rates for negative ions, extending those results to neutral atoms, and applying those results to seeking ways to enhance high order harmonic yields; and investigating two-electron effects in high order harmonic generation by short-pulse lasers. Graduate students and postdoctoral researchers involved with this project are given a broad education in theoretical atomic physics, first hand experience in all aspects of scientific communication, and in teaching undergraduates at a large AAU Land Grant university. Project results are not only published in leading physics journals and presented at national and international meetings, but are also periodically distilled and integrated with related work by others in review articles written by the PI and collaborators. All graduate students and postdoctoral researchers involved with this project in the past have been sought after by a variety of other employers, including technology companies, medical researchers, and other leading AMO theory groups. The basic research supported by this project contributes broadly to our understanding of means to control matter on an atomic scale. Our work on increasing the intensities of high order harmonics may one day lead to sources of coherent x-rays, thus providing a new means for visualizing living biological structures as well as nanoscale materials structures. Our investigations involving attosecond pulses of electrons may lead to ways of resolving electron motion both temporally and spatially. A workshop on attosecond science at the Kavli Institute for Theoretical Physics co-organized by the P.I. in 2006 has helped to enhance the infrastructure for research in this emerging new discipline. The P.I.'s co-editing of a special focus issue of New Journal of Physics on attosecond science in 2008 is evidence of his continuing service to the research community.