Strong Field and Ultrafast Atomic and Molecular Processes

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Intellectual Merit: This project focuses on understanding theoretically the interaction of intense coherent laser radiation with electrons, atoms, and molecules and on investigating the use of ultrashort (attosecond scale) laser or electron pulses to image the time-dependent motion of electrons in atoms and molecules. The interactions of electrons with both intense laser fields and with atomic and molecular potentials are difficult to describe accurately; also, their interactions with ultrashort laser or electron pulses must be described time-dependently. We have developed a number of theoretical approaches to overcome these difficulties. In particular, we have solved essentially exactly the problem of a weakly bound electron in a short-range potential interacting with an intense laser field and the results obtained for this particular system can be accurately generalized to the case of other, more complex atomic and molecular systems. Our investigations include: (1) using short (attosecond scale) electron pulses as both temporal and spatial probes of electron motion in both atoms and molecules; (2) investigating the utility of using intense lasers to assist or induce electron scattering from atoms, electron recombination with atoms, and electron bremsstrahlung (radiative) processes in the vicinity of atoms; (3) developing analytic formulas for laser-induced high-order harmonic generation for the heretofore analytically unexplored cases of elliptically-polarized laser fields, crossed two-color laser fields, and chirped, few-cycle laser fields, both for atoms and for asymmetric diatomic molecules. Broader Impacts: 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 Big 10 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 material structures. Our investigations involving ultrashort (attosecond) pulses of electrons may lead to ways of resolving electron motion both temporally and spatially. The P.I.'s membership on the American Physical Society's Publications Oversight Committee (2010-2013) and on the Science Advisory Board of the Max Planck Institute on the Physics of Complex Systems (2007-2013), a major theoretical atomic physics center in Dresden, Germany, is evidence of his continuing service to the scientific community.