Proposal for precision wavelength measurement of the Ni-like gadolinium x-ray laser formed during the interaction of a nanostructured target with an ultrashort laser beam

The wavelengths of the 3d ⁹4d [J = 0]–3d ⁹4p [J = 1] transitions of x-ray lasers in Ni-like sequence ions with nucleus charges Z  ⩽  79 are refined. The results of calculations are within the experimental error. It was found that the wavelengths of $3d_{3/2}^{9}4d_{3/2}^{}$ [J = 0]–$3d_{3/2}^9$4p _1/2 [J = 1] and $3d_{3/2}^9$4d _3/2[J = 0]–$3d_{5/2}^9$4p _3/2[J = 1] transitions in Sm³⁴⁺ and Gd³⁶⁺, respectively, are in the range of 6.70–6.75 nm. Exactly for this narrow range, multilayer mirrors with high reflectance are developed.

The gain of the x-ray laser with λ = 6.748 nm in Gd³⁶⁺ is calculated under the assumption that plasma is formed during the interaction of a nanostructured (cluster-like) gadolinium target with high-intensity pump laser radiation. The optimum plasma density, temperature, length, and pump parameters are determined to achieve the highest Gd³⁶⁺ ion fraction and emission quantum yield of ∼10¹³ photons. (letter)