Beginnings

The first order-of-magnitude estimate of an X-ray laser pumping scheme appeared in 1967, in the paper entitled “Some Approaches to Vacuum UV and X-ray Lasers” by M.A. Dugay and P.M. Rentzepis [1]. The authors examined the possibility of creating population inversions in the XUV energy range by photo-ionizing neutral atoms in such a way that the created ions present an inner shell vacancy. A large number of ions, simultaneously prepared in a time interval shorter than the vacancy lifetime, would offer the population inversion necessary to generate a laser action. This pumping scheme was illustrated by order-of-magnitude calculations for a sodium vapor tube and for a solid copper rod, from which laser emission could be expected at 37.2 nm and 0.154 nm, respectively.