Laser source: The formation of a Bose-Einstein condensate. As experts lower the temperature of the atoms, the cloud on the left gradually localises to form a pure condensate in the right-hand image. These atoms are just one hundred billionths of a degree above absolute zero.
Credit: ANU
SYDNEY: Australian researchers have created an atom laser that can refuel itself, bringing us a step closer to using them for practical applications, similar to the way optical lasers are currently used in medical and other technologies.
The results, by researchers at the Australian National University (ANU) in Canberra, were published at the weekend in the journal Nature Physics.
Atoms, not light
Atom lasers beam bright atoms rather than light. They were first developed by Nobel Prize-winning U.S. researchers a decade ago, but their uses have been limited to research as the lasers quickly run out of their source of atoms.
The ANU researchers say their laser can refuel itself similar to the way a bucket of water is recharged by a tap.
"Our work paves the way for a potentially unlimited source of ultra-high brightness atoms. It's like going from a trickle of atoms leaking from a thimble to turning on an atom tap," said Nick Robins, lead author of the research and joint head of the Atom Laser Group at the ANU.
Atom lasers can very accurately measure gravity, electric and magnetic fields and acceleration and rotation. They have practical applications in devices used for mineral research and navigation both on Earth and in space. Using atoms lasers in a device that measures rotation, for example, could lead to the development of spacecraft that don't need to relay signals to find their location, or missiles that could secretly track themselves.
How it works
The atom laser uses a source of atoms cooled to 100 billionths of a degree above absolute zero (–273°C), where they enter a state known as Bose-Einstein condensate (BEC). In this state, the atoms act like one giant super atom rather than a stream of separate atoms. Waves from the atoms form the laser in the same way as light waves are focussed in an optical laser.
To refuel the laser, the researchers created two clouds of BEC, one on top of the other. The top cloud acts like a tap, refilling the bottom cloud with atoms. The bottom cloud, from which the laser emanates, is known as the lasing mode.
The researchers needed to ensure the refuelling atoms from the top cloud were indistinguishable from those in the lasing mode, as BEC clouds are extremely sensitive to change.
"We had to overcome a series of theoretical and technical hurdles, mainly related to the delicate nature of the Bose-Einstein condensate. It only exists at near absolute zero and is hard to maintain," said Robins.
Practical device
Co-author John Close, quantum physicist and co-leader of the ANU group, said so far atom laser experiments have only had the lasing mode, so the cloud eventually drains. "The idea is that we are trickling the atoms down from the upper source. The BEC cloud at the top acts like a tap keeping the 'bucket' [the lasing mode] refilled."
Close said what distinguished their research was their efforts to make atom lasers a practical device. "Optical lasers are studied, but they are also in the real world, cutting eyeballs, scanning checkout items and so on. We're very much going down the path of making something useful," he said.
The team expect to have a device based on the laser within two years.
