Scaled-energy spectroscopy of barium autoionizing Rydberg atoms in an electric field

Abstract

Scaled-energy spectra were measured in autoionizing Rydberg series converging to both the 5d_3/2- and 5d_5/2- ionization limit for the same range of scaled-energy values. Surprisingly, even above the classical field ionization limit periodic orbits could be observed. Complex excitation spectra of Rydberg atoms in a strong electric field (or oscillator strength distributions) at first sight do not appear to contain any accessible information. However, when recorded at constant scaled energy (i.e., changing the external field strength while scanning the laser frequency) the Fourier transforms (FT) of these spectra show a remarkable simplicity. A limited set of peaks appears in the so-called action spectrum, where each peak can be related to a classical periodic orbit of the electron in configuration space.