Doppler Limit
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: a limit for the temperature which is achievable with certain laser cooling techniques
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DOI: 10.61835/rda Cite the article: BibTex plain textHTML Link to this page! LinkedIn
The temperature achievable with Doppler cooling, a type of laser cooling, is given by the Doppler limit:
$${T_{\rm{D}}} = \frac{{\hbar \gamma }}{{2{k_{\rm{B}}}}}$$where ($\gamma$) is the inverse upper-state lifetime, related to the natural linewidth of the atomic transition, and ($k_\textrm{B}$) is the Boltzmann constant. Typical values for the Doppler limit are of the order of hundreds of microkelvins.
Temperatures below the Doppler limit can be reached, e.g. with Sisyphus cooling or with velocity-selective coherent population trapping. It is then possible to reach the lower recoil limit, or even lower temperatures.