Coherently controlled Rydberg atoms as gain medium for an X-ray laser

The application of atomic Rydberg states as the initial medium in an x-ray laser based on optical field ionization is discussed. After laser preparation of the Rydberg state a second, intense short laser pulse ionizes the core electrons. The Rydberg electron can survive this laser pulse with high probability. Thus the ions that are produced still have one bound electron in a highly excited Rydberg state. The problem of electron-ion recombination, which is required to produce ionic Rydberg states in any recombination x-ray laser scheme, and which is generally slow due to high electron temperatures, is thus circumvented. Calculations on coherently excited lithium Rydberg states are presented which show the evolution of the electron wavepacket after the ionization of the inner electrons. The stability of the Rydberg electron is discussed and experiment al evidence for this stability obtained on the photoionization of barium Rydberg states is presented. Finally the feasibility of implementing the proposed scheme under high density plasma conditions is discussed.