Atoms acting as lasers
CANBERRA, Australia – An atom
laser that behaves exactly like a light laser has opened up new possibilities in
applications such as holograms.
A research team from The Australian National University ARC Centre
of Excellence for Quantum-Atom Optics has shown that a beam of helium atoms can
be made to have properties similar to a coherent laser light beam. The atom study
confirms a theory first developed for light nearly 50 years ago by Roy Glauber,
winner of the 2005 Nobel Prize in physics.
When scientists measure the time between the arrivals of the photons
in laser beams, they find that the photons are randomly spaced, with all arrival
times between photons equally probable. However, incoherent sources – such
as lightbulbs – exhibit photon bunching, where it is more likely that photons
will arrive within a short time of each other. The bunching is manifested by photons
arriving in pairs (second order) or in triplets (third order).
The investigators realized that if they made the atoms extremely
cold – within one-millionth of a degree of absolute zero – they could
force them to march in step, creating an atom laser that behaves coherently exactly
as a laser beam composed of photons. This showed, for the first time, that the same
second- and third-order-coherence properties of lasers also apply to atoms. In addition,
the cold atom laser demonstrated random distribution of arrival times with no bunching,
indicating that it was perfectly coherent.
When the atoms were warmed back up, the group found that they
no longer behaved coherently and once again exhibited bunching in pairs and triplets.
The research appeared in Science, Feb. 25, 2011 (doi: 10.1126/science.1198481).
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