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Jiliang xuebao

Experiments and Considerations of Realizing Cold Cesium Atomic 74 cm Fountain

Tianchu Li

Published Jan 1, 2003• 0 citations
OpenAlex

Abstract

The realization of 74 cm fountain of atomic clouds, obtaining fluorescence signal of time of flight with S/N～200, on NIM4# laser cooling - Cs atomic fountain clock is described. The improvements concerning launching - falling - signal detection are introduced, launching parameters listed, the fountain experiments are reported, and some preliminary discussions given.

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The realization of 74 cm fountain of atomic clouds, obtaining fluorescence signal of time of flight with S/N～200, on NIM4# laser cooling - Cs atomic fountain clock is described. The improvements concerning launching - falling - signal detection are introduced, launching parameters listed, the fountain experiments are reported, and some preliminary discussions given.
We report a novel method for temperature measurement in a cesium fountain clock and experimental investigation about its dependence respect to diverse operational parameters. The temperature of the Cs atomic cloud is inferred from the width of the velocity distribution, which is obtained from two measurements in different regions of the spatial distribution of the atomic cloud using the time of flight (TOF) method. We use a simple process to determine the velocity distribution by calculating the square speed point by point from these two TOF signals. This new method is demonstrated to characterize the temperature of the Cs atoms on the CENAM Cs fountain clock. The minimum temperature reached in the CENAM Cs fountain clock is 612(193) nK.
We report here on progress towards the realization of an atomic frequency standard using a fountain of laser cooled cesium atoms. We have recently observed Ramsey fringes on the 9.2 GHz clock transition and have begun preliminary work aimed at characterizing our fountain. This paper describes briefly the apparatus, discusses our current work and near-term directions. We conclude with a brief discussion of a laser system being built to realize two-dimensional Raman cooling or Raman velocity selection for cooling below the single photon recoil limit. This system will be used either in our fountain or in a cold-atom clock to be flown on the International Space Station.
To improve the signal to noise ratio (SNR) and the short-term stability of cesium atomic fountain clocks, the work of two-laser optical pumping is presented theoretically and experimentally. The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the | F = 4, mF = 0〉 clock state with a shortened cycle time. Two π-polarized laser beams overlapped in the horizontal plane have been applied after launching, one is resonant with | F = 4〉 → | F′ = 4〉 transition and the other is resonant with | F = 3〉 → | F′ = 4〉 transition. With optical pumping, the population accumulated in the | mF = 0〉 clock state is improved from 11% to 63%, and the detection signal is increased by a factor of 4.2, the SNR of the clock transition probability and the short-term stability are also improved accordingly.
An atomic cesium fountain has been designed for a new primary standard of frequency in China. Cold atomic clouds collected in the magneto-optical trap (MOT) were previously reported (1995). To further improve the performance of the MOT we have optimized the laser-optical system and operation of the MOT. Some optical elements were replaced with new ones with better quality; frequency stabilization of lasers and arrangement of the optical system was modified; and polarization maintaining (PM) optical fibers were adopted to transfer lights from the optical system to MOT. We also installed the fluorescence detecting - amplifying assembles to take the time of flight (TOF) measurement of the cold atoms.