Strong Field and Ultrafast Atomic and Molecular Processes

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This project focuses on understanding theoretically the interaction of intense coherent laser radiation with electrons, atoms, and molecules and on investigating the use of ultrafast laser or electron pulses to image time-dependent electronic processes in atoms and molecules. The basic research supported by this project contributes broadly to our understanding of means to control matter on an atomic scale. Investigations involving ultrashort pulses of electrons may lead to ways of resolving electron motion in atoms and molecules both temporally and spatially. In "seeing" how electrons move and interact with light, scientists will be better able to eventually control the electron motion, thereby leading to important applications in improving the efficiency of such key processes as solar energy conversion and photosynthesis, and in combining optical and electronic processes (e.g., the emerging new field of optoelectronics) to make much faster switches that in turn would enable much faster computers. The analyses of ways to increase 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. 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 processes included in this project are difficult to treat theoretically because 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. This group has developed a number of theoretical approaches to overcome these difficulties. In particular, they 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 atomic and molecular systems. They have also developed theoretical approaches for simulating the interaction of ultrashort electron pulses with time-dependent states of atoms and molecules. Specific investigations supported in this project include: (1) using ultrashort duration electron pulses as both temporal and spatial probes of electronic motion in atoms; (2) investigating intense laser-assisted or laser-induced electron scattering, electron recombination, and electron bremsstrahlung processes; (3) developing analytic formulas for high-order harmonic generation for molecules for both long and short laser pulses in the long-wavelength approximation, investigating analytic formulas for two-color harmonic generation spectra in atoms, and investigating analytically zeptosecond interference features in harmonic spectra produced by long-wavelength lasers; and (4) investigating finite pulse effects in intense laser acceleration of electrons bound in highly-charged ions, and developing a combined quantum description of tunneling ionization with a classical relativistic description of laser acceleration of electrons initially bound in highly-charged ions.