Rydberg x-ray laser based on inner-electron optical-field ionization

An alternative scheme for a recombination x-ray laser based on optical-field-induced ionization is presented. The initial state in the ionization process is an atomic Rydberg state (n = 8) instead of the atomic or the ionic ground state. The intense optical laser field ionizes the core electrons, but because of various stabilization mechanisms the Rydberg electron is not ionized. The ionic Rydberg state will act as the initial state of a decay process leading to x-ray emission. The problem of slow recombination of hot electrons into Rydberg states, which frustrates efficient x-ray lasing, is thus circumvented. The feasibility of the proposed scheme for a H-like Li x-ray laser is discussed in detail. Experimental evidence for the proposed mechanism of inner-electron ionization is presented in the case of Ba Rydberg atoms.