Rydberg-electron wave-packet dynamics in parallel electric and magnetic fields and evidence for stabilization

The dynamics of short-lived quasibound Rydberg-electron wave packets above the classical field-ionization limit are investigated in the presence of parallel electric and magnetic fields. The observed variations in relative peak intensities in the recurrence spectra are understood both in terms of a quantum-mechanical picture and in terms of the classical electron trajectories. The linear Zeeman term causes the Rydberg wave packet to rotate around the magnetic field axis. This rotation is observed experimentally as a sinusoidal intensity modulation superimposed on the periodic structure which is attributed to motion in the angular-momentum coordinate. The diamagnetic term stabilizes the Rydberg wave packet. This stabilization is observed experimentally as an increase in the recurrence peak intensities and the observation of recurrences after longer delays (up to twice as long as in the absence of the magnetic field). Classical trajectory calculations identify the dominant closed orbits which contribute to the experimental recurrence spectra.