LASER Cooling

John K Clark (
Wed, 4 Dec 1996 12:38:57 -0800 (PST)


On Mon, 2 Dec 1996, Lyle Burkhead wrote:

>What mechanism could the cell use to pump heat out of a
>small region?

Well, LASERS keep getting smaller and people are talking about Quantum Dot
LASERS, they would be mighty small, so maybe you could use LASER cooling.
You tune a LASER beam to a frequency slightly below the Quantum absorption
frequency of an atom, if the atom is motionless or moving away from the LASER
it will not be able to absorb a photon from the LASER, but if the atom is
moving toward the LASER the frequency of the photon the atom sees will be
shifted slightly higher due to the Doppler effect. The photon is now right at
the Quantum absorption frequency, the atom will swallow it whole including
the momentum of the photon, this will slow the atom down.

Yes, now that the atom is excited and no longer in its ground state eventually
the atom will re emit the photon, but the direction is random, it's just as
likely to cool the atom further as heat it, so this has no net effect on the
cooling process. If you have 6 such LASER beams one for, forward, backward,
right, left, up, down, you can cool things to very close to absolute zero.
This has already been done, it's how a Bose Einstein condensate was made
last year.

John K Clark

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