Electron emission of cesium Rydberg (n»21) 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.

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Journal Phys. Rev. Lett.
Vrijen, R. B, Lankhuijzen, G. M, & Noordam, L. D. (1997). Delayed electron emission in the ionization of Rydberg atoms with half-cycle THz pulses. Phys.Rev.Lett., 79, 617–620.