An intense, highly collimated continous cesium fountain
The realisation of cold and slow atomic beams has opened the way to a series of precision measurements of high scientific interest, as atom interferometry, Bose-Einstein Condensation and atomic fountain clocks. The latter are used since several years as reference clocks, given the high performance that they can reach both in accuracy and stability. The common philosophy in the construction of atomic fountains has been the pulsed technique, where an atoms sample is launched vertically and then falls down under the effect of the gravity. The Observatoire de Neuchâtel had a different approach and has built a fountain clock (FOCS1) operating in a continuous mode. This technique offers two main advantages: the diminution of the undesirable effects due to the atomic density (e.g. collisions between the atoms and cavity pulling) and to the noise of the local oscillator (intermodulation effect). To take full advantage of the continuous fountain approach however, we need to increase the atomic flux. The techniques chosen to reach this goal are an efficient transverse collimation together with more atoms to begin with. Here we report on a study of different transverse collimation techniques performed in a two-dimensional phase stable optical lattice (namely gray molasses and magnetically induced laser cooling) as well as the development and characterisation of a 2D-magneto-optical trap used to load the fountain. Best performances are reached in a 2D+-MOT configuration of such a pre-source, for which we detect an atomic flux 20 times greater than the one measured when the fountain is loaded by a Cs vapour. This gain could improve the atomic clock stability by a factor 6. An even better stability is expected after introducing a pre-cooling stage before performing the transverse collimation. This new configuration is currently under investigation and will be implemented in a second continuous fountain (FOCS2).
Thèse de doctorat : Université de Neuchâtel, 2006 ; 1876
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