Photon- and Electron-Driven Atomic Collision Processes: General Theory and Accurate Numerical Calculations

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This project deals with the interaction of light (mostly lasers) and charged particles (mostly electrons) with atoms and ions. The results are of importance for the understanding of fundamental collision dynamics, and they also fulfill the urgent practical need for accurate atomic data to model the physics of stars, plasmas, lasers, and planetary atmospheres. The short-pulse intense-laser part of the project requires accurate solutions of the time-dependent Schroedinger equation on a numerical space-time grid. With the rapid advances currently seen in computational resources, such studies can now be conducted for realistic systems, as opposed to idealized models. This work is important to facilitate further developments in the imaging and control of submicroscopic reactions, which in turn are expected to have broad impact by reaching out from physics to chemistry and ultimately biology. Many experimental efforts worldwide are supported through the present project, which will also train a post-doctoral associate and a number of research students.Most of the numerical calculations will be based upon the non-perturbative R-matrix (close-coupling) method. In addition to the frequently-used but limited “single-active electron (SAE) model”, the group has access to some of the most sophisticated all-electron codes that are expected to provide accurate quantitative predictions, including for cases where SAE is known to fail. These include the R-matrix with Time Dependence (RMT) suite of codes developed in Belfast and the highly flexible B-spline R-matrix (BSR) implementation with non-orthogonal orbital sets developed at Drake University. While BSR was originally designed for time-independent processes (atomic structure, electron collisions with atoms and ions, weak-field photoionization), the group will continue to work on interfacing RMT with output (multi-electron Coulomb and dipole matrix elements) generated by BSR. This is expected to result in an accurate and efficient time-propagation scheme for solving the time-dependent Schroedinger equation for the interaction of intense short-pulse lasers with complex atomic targets. Even though the problems in their entirety are very complex, continued student involvement in testing the numerical methods and visualizing the results is expected.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.