Stark wave packets viewed with half-cycle pulses

We have directly observed the motion of Rydberg wave packets of cesium in a static electric field through their ionization by half-cycle electromagnetic field pulses. Both Kepler orbital motion as well as angular motion, i.e., the periodic change in orbit ellipticity due to angular momentum evolution, can be clearly seen. The latter has never been directly observed, because conventional photoionization and two-pulse optical interferometry experiments are only sensitive to dynamics near the ion core and not when the wave packet has a high angular momentum.