HIGH-GAIN NI-LIKE X-RAY LASER-DRIVEN BY 2 LASER-PULSES

An Ni-like x-ray laser scheme with a double-pulse laser driver is sugg ested for increasing the gain of the 3p(6)3d(9)4d --> 3p(6)3d(9)4p and new 3p(5)3d(10)4p --> 3p(5)3d(10)4s lasing transitions, and of a poss ible 'water-window' inner-shell 3d --> 3p (3p(5)3d(10)4p --> 3p(6)3d(9 )4p) transition. The calculated gain coefficients for tantalum and tun gsten are in agreement with the published experimental results for the 4d --> 4p transitions. Inner-shell lasing in a material with a relati vely low Z, such as caesium, is suggested on the basis of this transit ion scheme. It is shown that the use of nonthermal electron pumping (b y the second laser pulse) leads to higher gains.