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arXiv · 2608.27097

Beyond-EUV spectrum of highly-charged gadolinium

M. L. Reitsma·J. Sheil·O. O. Versolato·E. V. Kahl·J. C. Berengut
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Abstract

We report ab initio relativistic calculations on the complex Gd$^{18+}$ and Gd$^{26+}$ highly-charged ions, which are relevant to beyond-extreme-ultraviolet (BEUV) light sources based on laser-produced gadolinium plasmas. Using the particle-hole configuration-interaction with many-body perturbation theory (CI+MBPT) method, we systematically saturate the $n=4$ configuration space and determine the influence of multiply excited states on the emissivity spectrum. For Gd$^{26+}$ we find behavior analogous to that of its isoelectronic counterpart Sn$^{12+}$, with strong contributions from multiply excited states, where even the quadruply excited states become significant at certain effective temperatures. In contrast, the industry-relevant 6.7 nm emission of Pd-like Gd$^{18+}$ is dominated by the singly excited $4d^{10} {\ }^{1}S_{0}$ -- $4d^{9}4f {\ }^{1}P_{1}$ transition, while multiply excited states primarily contribute to out-of-band emission. The calculated spectra show good agreement with experiment and demonstrate that the importance of multiply excited states depends strongly on both charge state and plasma conditions.

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M. L. Reitsma, J. Sheil, O. O. Versolato, E. V. Kahl, J. C. Berengut. 2026-08-27. Beyond-EUV spectrum of highly-charged gadolinium. https://arxiv.org/abs/2608.27097

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