Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences and their collaborators recently conducted the first experimental research on laser cooling and precision laser spectroscopy of Li-like ¹⁶O⁵⁺ion beams. They found that Li-like ¹⁶O⁵⁺ is the ion with the highest charge state, the highest transition energy, and the highest kinetic energy that has ever been directly laser-cooled.

Laser cooling and manipulation of ions in traps have proven to be powerful and valuable for atomic physics, precision metrology and fundamental symmetries studies. In addition, laser cooling is considered to be the most promising method to realize the phase transition and even crystalline ion beam regime at storage rings, which are of great interest to accelerator physics and precision measurements in atomic physics and nuclear physics. 

As of today, only a few ion species have been laser-cooled at heavy-ion storage rings due to the very short transition wavelengths in highly charged ions and the lack of suitable laser systems at those wavelengths.

In this study, researchers achieved laser cooling of bunched ¹⁶O⁵⁺ ion beams at relativistic energy at the experimental Cooler Storage Ring (CSRe) at the Heavy Ion Research Facility in Lanzhou (HIRFL). The initially injected and bunched ion beams were laser-cooled using a continuous-wave, single-mode narrow linewidth diode laser system. 

Besides, researchers simulated the longitudinal Schottky spectra of laser-cooled bunched ion beams with the multi-particle tracking method, providing valuable insights into the experimental observations. 

Moreover, researchers investigated the fine-structure splitting transition 2S1/2-2P1/2 in lithium-like O⁵⁺ in a laser spectroscopy experiment at CSRe. Using a Schottky resonator with very high sensitivity, they successfully identified the excitation resonance between the laser light and the ions.

The findings were published in Physical Review A, and Nuclear Instruments and Methods in Physics Research A, respectively. They pave the way for laser cooling and precision laser spectroscopy at the future large heavy-ion accelerators, such as the High Intensity heavy-ion Accelerator Facility in China and the Facility for Antiproton and Ion Research in Germany.