Work

Laser-fluence-dependent production of molecular thorium ions in different charge states for trapped-ion experiments

Year: 2025

Type: article

Abstract: Thorium ions and molecules, recognized for their distinctive nuclear and atomic attributes, are central to numerous trapped-ion experiments globally. Our study introduces an effective, compact source of thorium atomic and molecular ions produced via laser ablation of microgram-scale, salt-based samples. We thoroughly analyze the variety of ion species and charge states generated at varying laser fluences. Utilizing 10 µ g of thorium fluoride crystals and laser fluences between 1.00(5) and 6.75(35) J/ cm 2 , we produce thorium molecular ions ThF x 232 n + (with x = 0 – 3 and charge states up to n = 3 ), including ThF 2 + and ThF 3 + . These species are particularly relevant for spectroscopy; ThF 3 + is valuable due to its stable closed-shell configuration, while ThF 2 + , which is isoelectronic to RaF, offers a unique probe for studying nuclear structure and fundamental symmetries due to its simple electronic structure with a single unpaired electron. Density-functional-theory-based calculations of the electric charge distribution aid in understanding the formation of the observed species. Positive charges are found to be mainly located on the thorium atom, which points to an inhibition of immediate Coulomb explosion, thus supporting the existence of the observed ion species. The simplicity of the method and similarities among the actinide elements suggest that our approach will also be applicable to other actinide species.

Source: Physical Review A

DOI: 10.1103/ztxz-dwhk