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The recoil limit is the lowest temperature reachable with laser cooling methods which involve a permanent interaction of the cooled atoms with light. It is given by the equation
where λ is the wavelength of the light and m is the mass of the atoms. At this temperature, the thermal energy equals the energy of an atom with a momentum equal to the photon momentum. Typical values for the recoil limit of atoms are of the order of 1 μK.
The recoil limit can be approached (although not fully reached) with polarization gradient cooling (→ Sisyphus cooling). Temperatures below the recoil limit have been achieved with velocity-selective coherent population trapping, where atoms become trapped in an electronic state where they do no longer interact with light.
|||A. Aspect et al., “Laser cooling below the one-photon recoil energy by velocity-selective coherent population trapping”, Phys. Rev. Lett. 61 (7), 826 (1988)|
|||M. Kasevich and S. Chu, “Laser cooling below a photon recoil with three-level atoms”, Phys. Rev. Lett. 69 (12), 1741 (1992)|
|||H. Katori et al., “Magneto-optical trapping and cooling of strontium atoms down to the photon recoil temperature”, Phys. Rev. Lett. 82 (6), 1116 (1999)|
See also: Doppler limit, laser cooling, photons
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