Coherent stabilization of zero-electron-kinetic-energy states

The accuracy of zero-electron-kinetic-energy (ZEKE) photoelectron spectroscopy rests on the ultralong lifetimes of the high-n, high-l Rydberg states that are responsible for the ZEKE signal. However, a few-photon process cannot excite electrons directly from the low-l ground state to the high-l ZEKE manifold. In this paper we show that using the dynamics of Rydberg Stark states in slowly time dependent external fields it is possible to control coherently the angular momentum of Rydberg electrons, and therefore also their lifetime. We derive explicitly two different schemes based on simple, short electric dc pulses, which populate precisely those high-l, long-lived Rydberg states that are necessary for accurate ZEKE experiments. The high-l states that we construct are also Stark eigenstates, therefore a moderate dc external field can eventually enforce cylindrical symmetry and lock the ZEKE electrons in the stable, long-lived high-l manifold. (C) 1999 American Institute of Physics. [S0021-9606(99)01515-9].