Year: 2026
Type: preprint
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.
Source: arXiv (Cornell University)
Language: English
Topic: Atomic and Molecular Physics
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204529179