Atoms in a Bose-Einstein condensate can be manipulated with lightto form a highly directional atom laser, physicists at theCommerce Department's National Institute of Standards andTechnology report in March 12, 1999 issue of Science.
The NIST atom laser represents a significant step forward fromthe first atom laser demonstrated in 1997 at the MassachusettsInstitute of Technology in that its atoms stream forward in achosen direction as a very narrow beam. The direction of theearlier MIT atom laser beam was determined by gravity and had abig spread due to the tendency of the atoms to repel each other.
"The atom laser is as different from an ordinary atom beam as anoptical laser is from a flashlight. It now gives you for atombeams what you have had with laser light," says William D.Phillips, leader of the Laser Cooling and Trapping Group in theNIST Physics Laboratory. Steven Rolston, Kristian Helmerson,Edward Hagley and Jesse Wen, all of NIST; Lu Deng of GeorgiaSouthern University; and Mikio Kozuma, now at the University ofTokyo also worked on developing the atom laser. Their work wasfunded in part by the Office of Naval Research and the NationalAeronautics and Space Administration.
The NIST atom laser was made from a gaseous Bose-Einsteincondensate, an exotic form of matter first achieved in Boulder,Colo., in 1995 by NIST physicist Eric Cornell and University ofColorado physicist Carl Wieman. In the atom laser experiment atNIST in Gaithersburg, Md., scientists trapped sodium atoms in amagnetic field and cooled them to a millionth of a degree aboveabsolute zero at which point they began to Bose condense.
They further cooled the gas to about 50 billionths of adegree above absolute zero, so that nearly all the atoms becamepart of the condensate. In a Bose-Einstein condensate, a statethat Albert Einstein predicted more than 70 years ago, all atomsbehave as a single entity in which individual atoms areindistinguishable from one another.
Although practical uses of the atom laser could be years away,scientists are excited about the NIST invention and itspotential. "As when the optical laser was invented 40 years ago,the potential applications of the atom laser may not yet beapparent," says Phillips, a Nobel laureate for his work oncooling and trapping atoms with laser light.
Nevertheless, scientists anticipate being able to createholographic images producing any picture or pattern desired on aflat surface. This eventually may lead to improvements inlithography, the manufacturing technique for making exquisitelysmall features on computer chips. The atom laser may lead toimprovements in instruments that currently use an atom beam, suchas novel gyroscopes and atom interferometers used in research.Such instruments may one day be used in navigation or inprospecting for oil.
To make their atom laser, NIST scientists aim two optical lasersat the supercold Bose-Einstein condensate, one from the left sideand one from the right. The atoms absorb photons from one laserbeam and emit photons into the other laser beam. This processtransfers momentum to the atoms and gives them a kick in thedirection of one of the laser beams.
In order to select the direction of the atom laser beam, NISTscientists tune the optical lasers to slightly differentfrequencies. The atoms preferentially absorb photons from thehigher frequency laser and emit them into the lower frequencyone. Therefore, they move in a single direction, toward one laserand away from the other.
Although the atoms gain momentum from the laser beams, they arestill held in the trap by the magnetic field. In order to freethe atoms, which are like tiny magnets all pointing in the samedirection, NIST scientists have to change the atoms' orientationso they no longer feel the attraction of the magnetic field usedto confine them. Reorienting the atoms requires energy, whichscientists provide by increasing the difference between thefrequencies of the optical lasers.
By pulsing the lasers very quickly, the scientists are able tooverlap the small clumps of atoms that get kicked out of the trapwith each pulse, effectively making a continuous beam of atoms.By varying the intensity of the laser light, the scientists areable to create atomic laser beams of varying intensities at thechosen direction and speed.
The NIST work represents a significant step toward making a trulycontinuous atom laser. Since the NIST atom laser removes atomsfrom a Bose-Einstein condensate containing a finite number ofatoms, it eventually runs out of atoms. For a truly continuousatom laser, scientists would have to find a way to replenish theatoms in the Bose-Einstein condensate while removing the atomsthat make up the atom laser beam.
The NIST atom laser is very well collimated, that is the atomsstreaming out of the Bose-Einstein condensate remain as a verynarrow beam, much as light in a laser pointer spreads very littleeven across a large auditorium. The atom laser is about 60millionths of a meter wide, about the diameter of a human hair,and travels at about 6 centimeters per second.
NIST scientists look forward to better, more intense atom lasersbecoming important scientific and maybe even practical tools.
For more information and to see images of the atom laser, go tothe NIST Physics Laboratory's news page on the World Wide Web at http://physics.nist.gov/atomoptics.
As a non-regulatory agency of the U.S. Department of Commerce'sTechnology Administration, NIST promotes economic growth byworking with industry to develop and apply technology,measurements and standards through four partnerships: theMeasurement and Standards Laboratories, the Advanced TechnologyProgram, the Manufacturing Extension Partnership and the BaldrigeNational Quality Program.
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