The manufacture of a
Bose-Einstein condensate; where a collection of
atoms have the same wavelength (see
wave/particle duality) lead to experiments to produce a
beam of such atoms, in a manner similar to
laser where
photons of the same wavelength are emitted.
In an atom laser, the
magnetic trap containing the Bose-Einstein condensate is
analogous to the cavity of a conventional laser, and
radio waves or laser beams can be used to '
pump' the atoms, until they are emitted from the trap.
This was first achieved at
M.I.T in 1997 by the research group of
Wolfgang Ketterle, in this experiment radio waves were used to flip the
nuclear spin of atoms in the trap so they were no longer confined, so they simply 'fell' out of the trap. This produced not so much a beam, as a sequence of spreading output pulses, caused by the atoms mutual
repulsion forcing them apart.
The first directional,
collimated matter laser was produced in the
NIST physics lab. by
E.W. Hagley, et al in 1999. In this experiment a condensate of
sodium atoms were driven by optical
Raman pulses from two lasers between different
magnetic energy levels. Tuning the lasers to slightly different
frequencies allowed the experimenters to cause atoms to be emitted in one direction; towards that of the lower frequency laser. The atoms emit photons preferentially towards the high frequency laser, and less so towards the lower frequency one, which in a manner similar to a
rocket gives the atoms
momentum. By increasing the difference in frequency between the Raman lasers, the atoms can be transferred into an energy level where they no longer feel the trapping
potential, and they are then ejected from the bulk of the condensate, to form (in this experiment) a beam the thickness of a human
hair, moving at 6
centimeters per second.
The beam only lasts as long as there are atoms in the
condensate, to keep it going long enough to do really useful
work, a way would have to found to add atoms back into the condensate. Some examples of the useful work that could be done with good, continuous wave matter lasers are :-
1.
Holography, if these lasers could be used to make holograms of matter, that is patterns of pictures, on the surface of objects, this could lead to the production of features on
silicon chips much smaller than is possible with conventional
lithographic techniques.
2. Improve the precision of
atomic clocks, leading to benifits in all experiments that rely on accurate measurements.
3. Improvements in
atomic imaging
References :-
A Well Collimated Quasi-Continuous Atom Laser, E.W. Hagley, L. Deng, M. Kozuma, J. Wen, K. Helmerson, L. Rolston, and W. D. Phillips.
Science 12 March 1999
An output coupler for a
Bose-condensed atoms, M.-O. Mewes, M.R. Andrews, D.M. Kurn, D.S. Durfee, C.G. Townsend, and W. Ketterle,
Physical Review Letters 78, 582, 27 January 1997.
.