optical molasses


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optical molasses

[′äp·tə·kəl mə′las·əs]
(optics)
A viscous damping force exerted on neutral atoms by a pair of identical oppositely directed lasers tuned at a frequency below an atomic resonance.
A large number of atoms collected and cooled in a small volume at the intersection of the beams of three orthogonal pairs of such lasers.
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The ball of atoms is then launched by differential detuning of the two vertical laser beams to make a moving optical molasses.
The atoms travel from the optical molasses source region through a region that is used to detect atoms later in the process, and into the magnetically shielded C-field section of the fountain.
By converting the slowest atoms in the optical molasses into a "dark" state, in which they no longer absorb photons, the team was able to chill helium atoms to a mere 180 billionths of a degree above absolute zero, where the atoms moved at the terrapinlike pace of 2 cm/s.
Ashkin and Bjorkholm point out that the optical molasses produces what amounts to a new state of matter, an ultra-cooled gas.