Laser cooling made simpler, cheaper.

Laser cooling made simpler, cheaper

Scientists cooling atoms to near absolute zero no longer need laser systems costing thousands of dollars. with just two $200 diode lasers, physicists at the University of Colorado in Boulder have now chilled cesium atoms to 1.1 microkelvins, or about a million of a degree above absolute zero -- the coldest temperature ever achieved.

Laser-cooling studies have boomed in the last few years, repeatedly breaking temperature records (SN: 7/23/88, p.52). But those experiments required elaborate and expensive equipment. The Boulder group's technique "dramatically simplifies" laser cooling, assert Carl Wieman and his colleagues in the Sept. 24 PHYSICAL REVIEW LETTERS.

In the past, researchers heated atoms to create a fast-moving beam, then slowed them with a laser aimed against the flow of atoms. To complete the cooling, they mired the atoms in the "optical molasses" existing at the intersection of six crisscrossing laser beams.

Bypassing the first two steps, Wieman's team started with room-temperature atoms -- in this case, cesium vapor. No one has tried to do this before, Wieman told SCIENCE NEWS. The team also used far less expensive diode lasers -- similar to those in compact-disk players -- first to "catch" cesium atoms for study, and then to generate the cooling "optical molasses." The physicists managed to cage their record cold sample in a magnetic field for about 1 second, establishing another record.

Other experimenters have had difficulty trapping atoms at temperatures below 300 microkelvins because the atoms would leak out of the "optical molasses" in a fraction of a second. "In earlier [experiments], the cold atoms were freely falling in a vacuum. You couldn't hold on to them or do anything with them," Wieman says.

By locking for colder samples in place, "we can do a lot of experiments with cold atoms," he adds. Wieman is building a new apparatus that he thinks may hold the cold atoms for about 1 minute.

"There's a list of applications [for the new technique] as long as your arm," says Harold J. Metcalf of the State University of New York at Stony Brook. These include atomic spectroscopy, studies of low-energy atomic collisions, and verification of some fundamental processes predicted by quantum mechanics.

The new technique might also improve atomic clocks. Wieman says he and Stanford University physicist Steven Chu have a patent for an atomic clock that may achieve up to 100 times the accuracy of the most precise existing clocks.