Schematic of some classical trajectories in the process of the ionization of a Rydberg atom which is placed in an electric field F (or magnetic field B) that is oriented along the z axis and perpendicular to the detector plane. If the ionized electron absorbs a photon, the electron moves away from the nucleus with its initial outgoing angle, and the waves propagate outward in all directions. Some trajectories head directly downhill, other trajectories head uphill initially and then return to the nucleus. Thus, the outgoing wave can be described as an ensemble of classical trajectories.