Laser Cooling of Cesium Atoms in Gray Optical Molasses down to 1.1 µK

D. Boiron, A. Michaud, P. Lemonde, Y. Castin, C. Salomon

Laboratoire Kastler-Brossel and Collège de France, 24 rue Lhomond, Paris 75005, France

S. Weyers, K. Szymaniec, L. Cognet, A. Clairon

LPTF-BNM, Observatoire de Paris, 61 avenue de l'Observatoire, Paris 75014, France

Appeared in: Proceedings EQEC. 8-13 sept 1996, p. 173 (1996) (reference) (image)

Cooling in Grey Molasses (GM)1,2 occurs when the laser frequency is tuned to the blue side of a J --> J or J --> J-1 transition (\omega l - \omega at > 0). Some states are then not coupled to the laser light. A Sysiphus effect between coupled states \Psi C, which have spatially modulated light-shifts and uncoupled states \Psi NC which experience no light-shift, accumulates the atoms into \Psi NC with very low momenta, on the order of the photon recoil momentum.

Experiments are performed on the F=3 --> F=2 transition of the cesium D2 line. We show that GM have a lower ultimate temperature than that of J --> J+1 molasses. With a time-of-flight technique, we find a minimum temperature of 1.1±0.1 µK at low atomic density (vRMS = 8.3 mm/s = 2.4 vrecoil). We measure the lifetime of GM as a function of laser parameters and find cooling times on the order of 1 m/s. Finally, in spite of the accumulation of atoms into uncoupled states, we find a linear dependence of the temperature on the atomic density with a slope of 0.6 µK/(1010 at/cm3)4. We interpret this effect as being due to photon reabsorption within the cloud of cold atoms.

Figure 1 - Temperature of grey molasses as a function of atomic peak density.

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D. Boiron, A. Michaud, P. Lemonde, Y. Castin, C. salomon, S. Weyers, K. Szymaniec, A. Clairon, "Laser Cooling of Cesium Atoms in Gray Optical Molasses down to 1.1 µKelvin", Phys. Rev. A 53, p. R3734 (june 1996).