optical molasses (original) (raw)
Author: the photonics expert (RP)
Definition: an arrangement of laser beams used for cooling atoms or ions
quantum photonicsRelated: Doppler coolinglaser cooling
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DOI: 10.61835/aax Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn
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What is an Optical Molasses?
An optical molasses is a single-frequency light field which can be used to dampen atomic motion, based on the mechanism of Doppler cooling (one variant of laser cooling). Although an optical molasses is often used in the context of trapping, it does not include trapping itself.
In a simple one-dimensional version, an optical molasses is made with two counterpropagating laser beams, the frequency of which is tuned slightly below an atomic absorption resonance. As a result, a motion of an atom (or ion) in the direction of one of the beams will lead to a Doppler shift so that the absorption rate for the counterpropagating beam is increased, whereas the absorption rate for the opposite laser beam is reduced. Effectively there is a dissipative light force which is always directed opposite to the motion and therefore serves to reduce that motion.
A three-dimensional optical molasses can be made of six laser beams, propagating e.g. in the ($+X$), ($-X$), ($+Y$), ($-Y$), ($+Z$), and ($-Z$) directions. Such an arrangement can reduce the motion in any direction of space. It can therefore effectively reduce the temperature of an atomic (or ion) cloud. The standard temperature limit is the Doppler limit, but there are techniques to reach even substantially lower temperatures.
It is also possible to use different frequencies of the counterpropagating beams, effectively generating a moving optical molasses which tends to bring the particle velocities toward a certain value. Through the Doppler shift, particles moving with that velocity experience equal frequencies of all the waves.
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is an optical molasses?
An optical molasses is a special light field, typically made of multiple counter-propagating laser beams, which is used to slow down atoms or ions. This cooling effect is based on the mechanism of Doppler cooling.
How does an optical molasses cool atoms?
The laser light is tuned slightly below an atomic resonance. Due to the Doppler effect, an atom moving towards a laser beam absorbs more light from it than from the beam propagating in the opposite direction. This creates a net force which is always directed opposite to the atom's motion, thus damping it.
How do you create a three-dimensional optical molasses?
A three-dimensional optical molasses is made with six laser beams, arranged as three pairs of counter-propagating beams along three perpendicular axes. This configuration can effectively reduce the atomic motion in any direction.
What is a moving optical molasses?
A moving optical molasses uses different optical frequencies for the counter-propagating laser beams. This causes the atoms to be cooled towards a specific non-zero velocity instead of being slowed down towards zero velocity.
Bibliography
| [1] | S. Chu et al., “Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure”, Phys. Rev. Lett. 55 (1), 48 (1985); doi:10.1103/PhysRevLett.55.48 |
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| [2] | P. D. Lett et al., “Optical molasses”, J. Opt. Soc. Am. B 6 (11), 2084 (1989); doi:10.1364/JOSAB.6.002084 |
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