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AIP conference proceedings

Laser cooling of cesium atoms below 3 microkelvins

Christophe Salomon, Jean Dalibard, William D. Phillips, André Clairon, Saïda Guellati-Khélifa

Published Jan 1, 1991• 5 citations
Publisher

Abstract

We have measured the temperature of cesium atoms released from optical molasses. For a wide range of laser intensity and detuning from resonance, the temperature depends only on the intensity to detuning ratio. The lowest temperature achieved is 2.5±0.6 μK, which corresponds to an rms velocity of 12.5 mm/s or 3.6 times the single‐photon recoil velocity. This is, to our knowledge, the coldest kinetic temperature ever measured for three dimensional (3D) cooling. We then discuss the possibility of using such a cold sample of atoms for realizing a high performance atomic clock in a fountain geometry. In particular, a method for launching the atoms upwards, while maintaining the very cold temperature, is demonstrated.

DOI
10.1063/1.41003

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We have measured the temperature of cesium atoms released from optical molasses. For a wide range of laser intensity and detuning from resonance, the temperature depends only on the intensity to detuning ratio. The lowest temperature achieved is 2.5±0.6 μK, which corresponds to an rms velocity of 12.5 mm/s or 3.6 times the single‐photon recoil velocity. This is, to our knowledge, the coldest kinetic temperature ever measured for three dimensional (3D) cooling. We then discuss the possibility of using such a cold sample of atoms for realizing a high performance atomic clock in a fountain geometry. In particular, a method for launching the atoms upwards, while maintaining the very cold temperature, is demonstrated.
Optical molasses is a three-dimensional (3-D) configuration of laser beams used to laser-cool and to viscously confine neutral atoms. Atoms laser cooled in optical molasses reach temperatures much lower than the limit given by the original theories of laser cooling based on the Doppler effect. This cooling below the Doppler-cooling limit is now seen as being due to new laser cooling mechanisms not considered in the original theories. The dependence of the atomic temperature on parameters such as laser intensity and detuning shows good agreement between calculations performed in 1-D and experiments performed in 3-D. For cooling of Na and Cs atoms, the lowest observed temperatures correspond to rms velocities between three and four times the single photon recoil velocity. For Cs the temperature is 2.5 ± 0.6 μK and is the lowest temperature ever measured for 3-D cooling.
We report an experiment on the adiabatic cooling of 87 Rb atoms in an atomic fountain to a temperature as low as 1.5 μK, which is roughly twice the recoil temperature. The atomic fountain has the (1,1,1) optical geometry for cooling and launching of cold atoms. The atoms are first cooled in an optical molasses of 6 beams to 3.4 μK by polarization gradient geometry and then are adiabatically cooled by decreasing the intensity of laser from 1.8I s per beam to zero in 1 ms during the launching of cold atoms. We also study the dependences of atomic temperature on different laser parameters. The method we used is useful in any cold atom physics experiment.
We use velocity-selective Raman pulses generated by two diode lasers to cool cesium atoms in 1 dimension to an r.m.s. of 1.2 mm/s. This is about 1/3 of the single-photon recoil velocity v rec = ℏk/M , where ℏk is the photon momentum and M the atom's mass. The corresponding effective temperature is a factor of 9 below the single-photon recoil temperature given by k B T rec /2 = 1/2 Mv rec 2 . Because of the high cesium mass, this temperature is only (23 ± 5) nanokelvin, the lowest 1D kinetic temperature reported to date.