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 non-thermal electron pumping (by the second laser pulse) leads to higher gains.