PHOTOABSORPTION SPECTRA OF ATOMS IN PARALLEL ELECTRIC AND MAGNETIC-FIELDS

Measurements have been made of the absorption spectrum of Ba from the 6s6p P-1(1) level to states near the ionization threshold in parallel electric and magnetic fields. The absorption spectrum shows oscillatio ns superposed on a smooth background. Each oscillation is correlated w ith a closed orbit of the electron. At strong electric fields, traject ories are regular, and closed orbits form orderly patterns. For weak e lectric fields, trajectories are chaotic, and many more closed orbits are present. Many of these are produced by bifurcations as the electri c field is reduced.