Laser polarization gradient cooling below the Doppler limit

5 Laser polarization gradient cooling below the Doppler limit 

In experiments on the 3D Doppler cooling of Na atoms (Lett et al. 1988), it was found, by way of direct measurement of the velocity of the cooled atoms leaving the cooling region, that the temperature of the atoms could in actual fact be almost ten times lower the Doppler limit fiK. Moreover, there were observed a number 

Let the atom move at a small angle to the wavefront of the light, so that its velocity projection is 

Consider for the sake of definiteness an atom starting to move from the point z = A/8 (Fig. 5.12). Such an atom will cover a distance of A/4 in a time shorter than Tp, and so it will climb from the potential minimum to the maximmn, while residing at one and the same sublevel, as illustrated in Fig. 5.13. The probability that optical pumping will cause the atom to move from one sublevel to the other here becomes higher. But the spontaneous-decay time is much shorter than the optical-pumping 

during each optical-pumping cycle with a period Tp, the atom loses the energy related to the potential depth AE. The cooling force acting on a moving atom 

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