We have directly observed the motion of Rydberg wave packets of cesium
in a static electric field through their ionization by half-cycle ele
ctromagnetic field pulses. Both Kepler orbital motion as well as angul
ar motion, i.e., the periodic change in orbit ellipticity due to angul
ar 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
.