Recoil, cooling limit

Surprisingly, however, we found that the major limitation to our experimental accuracy was due to the recoil imparted by photons to atoms. The radiation forces are of course well-known, being used for laser cooling, nevertheless their effect in precision spectroscopy is often disregarded as the interaction time be-... 

The recoil limit can be overcome by a recently discovered cooling scheme called Raman cooling (Fig. 9.29). Here a stimulated Raman scattering process is used, which traverses from level 1 via a virtual level down to level 3. If the levels 1 and 3... 

The recoil velocity for a sodium atom is, as mentioned above, about 0.03 m/s, which would in thermodynamic language correspond to a temperature of about 2pK. However, the statistical nature of absorption and emission in a gas of atoms or ions leads to a certain heating of the gas and a corresponding Doppler width, which is of the order of few himdred pK. This is referred to as the Doppler limit for the cooling temperatm-e Td, which can be expressed as... 

J. Lawall, S. Kulin, B. Saubamea, N. Bigelow, M. Leduc, C. Cohen-Tajmoudji Three-dimensional laser cooling of helium beyond the singlephoton recoil limit. Phys. Rev. Lett. 75, 4194 (1995)... 

The two methods of demonstrative character considered above should be supplemented with the classical Doppler-cooling method for forbidden transitions with a very small radiative broadening 7. In the first experiments of this kind (Katori et al. 1999) with an ensemble of Sr atoms, a 3D-cooling temperature that was close to a single effective recoil was obtained, that is, the alternative cooling pathway shown on the left of Fig. 5.4 was realized. Moreover, in the case of polychromatic excitation, there is even a possibility of reaching a temperature below the recoil limit (Wallis and Ertmer 1989). 

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