Abstract
The high brilliance expected from X-ray Free-Electron Lasers (XFELs) now under construction makes the proposal of a photo-pumped soft X-ray laser again feasible. We present simulations of a photo-pumped three-body recombination laser at He-α (λ = 58.4 nm) and Ly-α (λ = 30.4 nm) in helium, pumped by the XFEL at DESY/Hamburg. A low electron temperature, and thus a high recombination rate are provided by adjusting the pump photon energy closely above the ionization potential of the lasing ion. Our simulations show that pump parameters obtainable by the DESY XFEL are sufficient to generate He-α laser gain of ≈ 100 cm−1 and similar gain for the Ly-α laser. The gain duration depends critically on density and pump intensity and is between 100 and 300 fs for both lasers. A saturated photo-pumped soft X-ray laser seems to be possible by irradiating a He gas puff with XFEL pulses in a travelling-wave arrangement. The realization of such a laser could provide a better understanding of the physics of photo-pumped lasers and thus help developing table top X-ray lasers. In addition, the beam parameters of the photo-pumped X-ray laser could be superior to those of the pumping laser.