Two-electron Rydberg Atom Studies

A simple vacuum chamber equipped with a short linear time-of-flight device for measuring both photoion and photoelectron flight times is located in the Ultrafast Laser Facility for the study of so-called 2-electron atoms. The atoms (alkaline earths) are introduced into the vacuum through resistive heating of a simple oven. Using multiple short laser pulses, both valence electrons are promoted from the atomic ground state to create doubly-excited Rydberg states.

Doubly-excited Rydberg atoms provide pristine laboratories for studying coherent processes of chemical interest. While inherently simpler, the dynamics of doubly excited two-electron systems are affected by processes analogous to those at work in molecular systems, e.g.(1) configuration interaction between different excited two-electron systems are affected by processes analogous to those at work in molecular systems, e.g.(2) configuration interaction between different bound dielectronic modes (2 e- atoms) vs. intra-molecular vibrational redistribution (IVR in molecules); and (3) autoionization (2 e- atoms) vs. predissociation (molecules). The chemical physics group is interested in the use of coherent, short pulses of light to create tailored electronic wavepackets that eventually decay via autoionization. These packets are designed to exploit the internal electron-electron interaction to enhance specific decay channels relative to others. An advantage of studying two-electron atoms rather than molecules is that the number of interacting two-electron modes is tunable by selecting the amount of energy that is placed in the atom. Laser excitation of wavepackets at energies just above the first ionization limit of the atom results in relatively simple, calculable dynamics. Conversely, excitation to energies just below the second ionization limit results in the coupling of an infinite number of bound and continuum decay channels. Experiments in CAMOS explore the entire range of parameter space in the two-electron dynamics and control problem.