Abstract

An atomic Rydberg electron wave packet above the saddle point of the combined Coulomb and static electric field potential [1], created by a short laser pulse, shows a few oscillations in angular momentum (l) and radial co-ordinate before escaping from the atomic potential [2]. Up to now, experimental studies on the dynamics of the wave packet focused on recurrences of wave packets to the atomic core. These studies have been carried out both in the (1) time and (2) frequency domain. (1) In optical pump-probe studies the overlap near the atomic core of the evolved wave packet with the initial wave packet is directly measured as a function of time. (2) These recurrences of the launched wave packet to the atomic core lead to resonant structure in the photoionization spectrum. We introduce a new device, the atomic streak camera, which measures directly the escape over the saddle point of the Rydberg electron in a static electric field. By measuring the time dependent leaking of the wave packet over the saddle point, instead of measuring recurrences to the atomic core we found that the life time of the Rydberg electron as measured by an optical technique is not the same as the time it takes the electron to leave the atom. Optical techniques measure how many recurrences to the core region the electron makes, and have no access to other parts of the atomic potential. Hence, while the electron might no longer be visible for optical techniques it can still be in the atomic potential, and ionization is not yet seen by the atomic streak camera.

© 1996 Optical Society of America