Physics:Recoil temperature
In condensed matter physics, the recoil temperature is a fundamental lower limit of temperature attainable by some laser cooling schemes, and corresponds to the kinetic energy imparted in an atom initially at rest by the spontaneous emission of a photon.[1] The recoil temperature is
- [math]\displaystyle{ T_\text{recoil} = \frac{\hbar^2k^2}{mk_\text{B}} = \frac{p^2}{mk_\text{B}}, }[/math]
where
- k is the magnitude of the wavevector of the light,
- m is the mass of the atom,
- kB is the Boltzmann constant,
- [math]\displaystyle{ \hbar }[/math] is the Planck constant,
- [math]\displaystyle{ p = \hbar k }[/math] is the photon's momentum.
In general, the recoil temperature is below the Doppler cooling limit for atoms and molecules, so sub-Doppler cooling techniques such as Sisyphus cooling[2] are necessary to reach it. For example, the recoil temperature for the D2 lines of alkali atoms is typically on the order of 1 μK, in contrast with a Doppler cooling limit on the order of 100 μK.[3]
Cooling beyond the recoil limit is possible using specific schemes such as Raman cooling.[4] Sub-recoil temperatures can also occur in the Lamb Dicke regime, where an atom is so strongly confined that its motion (and thus temperature) is effectively unchanged by recoil photons. [5]
References
- ↑ Metcalf and van der Straten (1999). Laser Cooling and Trapping. New York: Springer-Verlag. ISBN 0-387-98728-2.
- ↑ Cohen-Tannoudji, C. (2004). Atoms in electromagnetic fields (2nd ed.). Singapore: World Scientific. ISBN 978-9812560193. https://archive.org/details/atomsinelectroma0000cohe.
- ↑ Cohen-Tannoudji, Claude N. (1 July 1998). "Nobel Lecture: Manipulating atoms with photons". Reviews of Modern Physics 70 (3): 707–719. doi:10.1103/RevModPhys.70.707. Bibcode: 1998RvMP...70..707C.
- ↑ Reichel, J.; Morice, O.; Tino, G.M.; Salomon, C. (1994). "Subrecoil Raman Cooling of Cesium Atoms". Europhysics Letters 28 (7): 477. doi:10.1209/0295-5075/28/7/004. Bibcode: 1994EL.....28..477R.
- ↑ Eschner, Jürgen (2003). "Laser cooling of trapped ions". J. Opt. Soc. Am. B 20 (5): 1003–1015. doi:10.1364/JOSAB.20.001003. Bibcode: 2003JOSAB..20.1003E.
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