Delayed Electron Emission in the Ionization of Rydberg Atoms with Half-Cycle THz Pulses

Electron emission of cesium Rydberg $\left(n\approx 21\right)$ atoms ionized with half-cycle THz pulses is investigated using an atomic streak camera. The THz pulses have a peak electric field of 17 kV/cm and a duration of less than 1 ps. It is found that the atoms do not always emit their electrons instantaneously. Under certain conditions up to 50% of the emitted electrons are ejected 11 ps after the time of interaction. The delayed electron emission shows a strong dependence on the direction in which the electrons are kicked, and is interpreted as scattering off the atomic core.