Overview
This study reports on ab initio relativistic calculations conducted on highly-charged gadolinium ions, specifically Gd$^{18+}$ and Gd$^{26+}$. These ions are relevant to the development of beyond-extreme-ultraviolet (BEUV) light sources, which are based on laser-produced gadolinium plasmas. The research employed the particle-hole configuration-interaction with many-body perturbation theory (CI+MBPT) method to systematically explore the $n=4$ configuration space and determine the influence of multiply-excited states on the emissivity spectrum of these ions.
Research Context
The context for this research lies in the development of beyond-extreme-ultraviolet (BEUV) light sources. Such sources are conceptualized to operate using laser-produced gadolinium plasmas. Understanding the spectroscopic properties, particularly the emissivity spectrum, of highly-charged gadolinium ions like Gd$^{18+}$ and Gd$^{26+}$ is crucial for optimizing and characterizing these light sources.
Approach
The researchers utilized an ab initio relativistic calculation approach. The specific computational method employed was the particle-hole configuration-interaction with many-body perturbation theory (CI+MBPT). This method allowed for a systematic saturation of the $n=4$ configuration space. The primary objective of this computational approach was to ascertain how multiply-excited states contribute to the overall emissivity spectrum of the highly-charged Gd$^{18+}$ and Gd$^{26+}$ ions.
Findings
- For the Gd$^{26+}$ ion, the study observed behavior analogous to its isoelectronic counterpart, Sn$^{12+}$. This behavior included strong contributions from multiply-excited states to its emissivity spectrum.
- A significant appearance of even quadruply-excited states was identified in Gd$^{26+}$ at certain effective temperatures.
- In contrast, for the industry-relevant 6.7 nm emission of Pd-like Gd$^{18+}$, the emissivity was predominantly influenced by the singly excited $4d^{10}$ $^{1}S_{0}$ - $4d^{9}4f$ $^{1}P_{1}$ transition.
- Multiply-excited states in Gd$^{18+}$ primarily contributed to out-of-band emission, rather than the primary 6.7 nm emission.
Why This Matters
The findings from this ab initio relativistic calculation offer insights into the fundamental atomic physics governing highly-charged gadolinium ions. Understanding the contributions of singly and multiply-excited states to the emissivity spectra of Gd$^{18+}$ and Gd$^{26+}$ is directly relevant to the development and characterization of beyond-extreme-ultraviolet (BEUV) light sources, particularly those based on laser-produced gadolinium plasmas.