Advances Toward Inner-Shell Photo-Ionization X-Ray Lasing at 45 A

摘要

The inner-shell photo-ionization (ISPI) scheme requires photon energies at least high enough to photo-ionize the K-shell, approximately 286 eV, in the case of carbon. As a consequence of the higher cross-section, the inner-shell are 'selectively' knocked out, leaving a hole state 1s2S(sup 2)2p(sup 2) in the singly charged carbon ion. This generates a population inversion to the radiatively connected state 1s(sup2)2s(sup 2)2p in C+, leading to gain on the 1s-2p transition at 45 angstroms. The resonant character of the lasing transition in the single ionization state intrinsically allows much higher quantum efficiency compared to other schemes. Competing processes that deplete the population inversion include auto-ionization, Auger decay, and in particular collisional ionization of the outer-shell electrons by electrons generated during photo-ionization. The competing processes rapidly quench the gain. Consequently, the pump method must be capable of populating the inversion at a rate faster than the competing processes. This can be achieved by an ultra-fast high intensity laser that is able to generate an ultra-fast, bright x-ray source.