Using the XFEL to drive gain in L-shell systems using photoionization processes

Six years ago an inner-shell X-ray laser was demonstrated at 849 eV in singly ionized neon using the X-FEL at 960 eV to photo-ionize the 1s electron in neutral neon followed by lasing on the 2p - 1s transition in singly-ionized neon. It required a very strong X-ray source that could photo-ionize the 1s (K-shell) electron on a time scale comparable to the intrinsic auger lifetime of 2 fsec. We extend this work from K-shell to L-shell transitions. We show how the XFEL could be used photo-ionize L-shell electrons to drive gain on n=3-2 transitions in singly-ionized Ar and Cu plasmas. For Ar this requires an XFEL above 250 or 330 eV with lasing on 3-2 lines at 220 and 310 eV. The Cu scheme requires an XFEL above 960 eV with lasing on 3d-2p lines at 928 and 948 eV. We will also discuss extending this work to photoionizing the M-shell with lasing on n=4-3 transitions in singly ionized neodymium.