The researchers used laser-based evaporative cooling to cool the negatively charged molecules

A team of physicists from Ruprecht-Karls University's Institute of Physics, in collaboration with colleagues from the Institute of Ionic Physics and Applied Physics at the University of Innsbruck, has developed a laser technique that selectively removes the most energetic ions from a sample, thereby cooling those that remain.

The team describes their method and its possible uses in a paper published in the journal Nature Physics. The Nature team also published a research highlight paper in the same issue outlining the team's work on the new work.

Cooling molecular ions has a wide range of applications in physics and chemistry research, including current work to better understand the chemistry of celestial bodies such as Saturn's moon Titan. Unfortunately, cooling negatively charged molecules has proven more difficult, and their uses are limited. In this new effort, the research team developed a technique that makes the process relatively simple.

The idea grew out of previous work involving the use of evaporative cooling, a technology related to evaporative coolers used to cool houses in dry areas. In this case, the technique is used to make antiprotons negatively charged by changing the shape of the trap containing them.

In the new work, the team first used a radio-frequency trap to keep the OH-anion sample at a temperature of about 370 K. They used a special type of laser called a single-optical separation laser to manipulate the anions in the trap. This is done by adjusting the laser to the desired threshold, which neutralizes the ions that pass through the laser beam, thus removing them from the trap.

As the process continues, those anions with the highest energy are slowly removed, leaving behind those with lower energy. This makes the entire trap and the remaining sample cooler. In subsequent experiments, the team found that they were able to optimize the process to cool the trap by several orders of magnitude.

The team concluded that their technique could be used for laboratory studies as well as research related to better understanding interstellar clouds or the atmospheres of celestial bodies such as Titan.

Source: Laser Network