# Infrared and visible laser spectroscopy for highly-charged Ni-like ions

## TL;DR

This paper demonstrates that visible and infrared lasers can effectively excite highly-charged Ni-like ions, enabling control of x-ray emission through photopumping, which was previously limited by energy mismatches.

## Contribution

It shows that the energy difference in Ni-like ions falls within the visible/IR range and that laser photopumping can significantly enhance x-ray line intensities.

## Key findings

- Laser photopumping increases ion level populations by two orders of magnitude.
- Visible/IR lasers can control x-ray emission in highly-charged ions.
- Theoretical calculations match limited experimental data.

## Abstract

Application of visible or infrared (IR) lasers for spectroscopy of highly-charged ions (HCI) has not been particularly extensive so far due to a mismatch in typical energies. We show here that the energy difference between the two lowest levels within the first excited configuration $3d^94s$ in Ni-like ions of heavy elements from $Z_N$=60 to $Z_N$=92 is within the range of visible or near-IR lasers. The wavelengths of these transitions are calculated within the relativistic model potential formalism and compared with other theoretical and limited experimental data. Detailed collisional-radiative simulations of non-Maxwellian and thermal plasmas are performed showing that photopumping between these levels using relatively moderate lasers is sufficient to provide a two-order of magnitude increase of the pumped level population. This accordingly results in a similar rise of the x-ray line intensity thereby allowing control of x-ray emission with visible/IR lasers.