This award will support a three-year cooperative research project in physics between Professor Walter R. Johnson, Department of Physics, University of Notre Dame, and Dr. Peter Zoller, Institute for Theoretical Physics, University of Innsbruck, Austria. The scientists and members of their research groups are collaborating in theoretical calculations regarding multiphoton ionization of atoms. The goal is to develop a modern theoretical basis for the description of this process, particularly in heavy atoms, including the effects of electron-electron correlation. The theoretical framework of the calculations will be the time-dependent Hartree-Fock method. Parallel to this work, a quantum defect theory of nonlinear optical processes will be developed. Current interest in multiphoton processes stems in large part from the availability of lasers. When certain atoms are subjected to high intensities of laser radiation, there is an unexpected, enhanced production of multiply charged ions. It is to explain such experimental results on a quantitative basis that both research groups wish to develop a modern theory of multiphoton ionization. At the present time, theoretical analyses of multiphoton ionization processes in atoms are usually based on the so-called independent particle model of the atom, which neglects interactions between the electrons (electron correlation effects). This model is simple, but does not give satisfactory results when applied to atoms with several electrons in the outer shells, such as the alkaline earth and rare gas atoms. Professor Johnson has developed methods for treating such atoms that go beyond the independent particle model. His expertise in electron correlation effects in atoms will be combined with that of Dr. Zoller, whose field of research is laser-atom interactions and multiphoton processes. Funds from this award would support necessary transportation and subsistence expenses for the U.S. principal investigator and a member of his research group. The Austrian Science Foundation (FWF) is providing counterpart support for the project and has approved the inclusion of this activity under the Memorandum of Understanding between the NSF and the FWF.
