Starting with Ba atoms in one Rydberg state we have observed the population of adjacent Rydberg states when the atom is exposed to an intense 1.5-ps laser pulse. The initial Rydberg state population is redistributed by a Raman-like two-photon process, rather than simply being photoionized. This population trapping, which is associated with stabilization against ionization, is described in terms of Rydberg antiwave packets.

• Received 3 December 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.1496