High-gain Ni-like x-ray laser driven by two laser pulses

An Ni-like x-ray laser scheme with a double-pulse laser driver is suggested for increasing the gain of the 3p⁶3d⁹4d → 3p⁶3d⁹4p and new 3p⁵3d¹⁰4p → 3p⁵3d¹⁰4s lasing transitions, and of a possible 'water-window' inner-shell 3d → 3p (3p⁵3d¹⁰4p → 3p⁶3d⁹4p) transition. The calculated gain coefficients for tantalum and tungsten are in agreement with the published experimental results for the 4d → 4p transitions. Inner-shell lasing in a material with a relatively low Z, such as caesium, is suggested on the basis of this transition scheme. It is shown that the use of nonthermal electron pumping (by the second laser pulse) leads to higher gains.