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

Drake University, Des Moines IA

Investigators

Abstract

This project deals with the interaction of charged particles (mostly electrons) and light (mostly lasers and synchrotron radiation) with atoms and ions. The results are not only important for the understanding of the fundamental collision dynamics, but 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 Schrödinger equation on a numerical space-time grid. With the rapid advances currently seen in computational resources, such studies can now be undertaken 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 several research students. Most of the numerical calculations will be based upon the non-perturbative close-coupling method, with the goal of pushing the expansion to convergence by including a sufficient number of low-lying physical bound states as well as pseudo-states to account for the coupling to the remainder of the infinite Rydberg spectrum as well as the ionization continuum. The group has contributed to the development, and hence has access to, some of the most sophisticated all-electron codes currently available to provide accurate quantitative predictions. These include the highly flexible B-spline R-matrix (BSR) implementation with non-orthogonal orbital sets to solve the close-coupling equations (developed in the PI's group at Drake University) and the R-matrix with Time Dependence (RMT) suite of codes developed in Belfast. While BSR was originally designed for time-independent processes (atomic structure, electron collisions with atoms and ions, weak-field photoionization), the group will adapt the output (multi-electron Coulomb and dipole matrix elements) from BSR to serve as input for RMT. This interface is expected to result in an accurate and efficient time-propagation scheme for solving the time-dependent Schrödinger equation for the interaction of intense short-pulse lasers with complex atomic targets. To assist in the understanding of the complex processes involved, simpler models such as the popular single-active electron approximation (SAE) will also be used for comparison between the predictions and the experimental data obtained in several collaborating laboratories. Continued student involvement in testing the numerical methods and associated computer codes, as well as 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.