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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Cesium fountain development at USNO

Eric A. Burt, Thomas B. Swanson, Christopher R. Ekstrom

Published Jan 22, 2003• 6 citations

Abstract

In this paper we discuss progress made at the U.S. Naval Observatory (USNO) towards building a cesium fountain atomic clock. In particular we will address the efficacy of a 4-beam optical lattice as an atom collection and launch mechanism. To date we have measured temperatures in a 4-beam lattice of 1.4(0.3) /spl mu/K and have launched atoms from this lattice to a height of just under a meter with a temperature of 1.7(0.1) /spl mu/K. We are able to collect 2.4/spl times/10/sup 6/ atoms using only the lattice beams and no magnetic fields. We have completed the design for and are in the process of fabricating all aspects of the fountain device including the collection region, the drift region, the microwave cavity and the magnetic shields. We present our progress to date including a discussion of our launch results and the design and testing of our magnetic shields.

DOI: 10.1109/freq.1999.840697

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We present results on the performance of two important subsystems for NIST-F2 - the second-generation atomic fountain clock at NIST. Firstly, we demonstrate the efficient capture of cesium atoms from a low-velocity intense source (LVIS) of atoms into an optical molasses. Our typical LVIS flux was 10/sup 10/ s/sup -1/. The initial molasses fill rate was R/sub t=0/ = 3.8(5)/spl times/10/sup 9/ s/sup -1/, which is consistent with 100% atom capture given the lifetime of our vacuum system. Secondly, recent results for our launch performance in the (1,1,1) fountain geometry are presented. We were able to cool the atoms to a temperature of 1.5 /spl mu/K with our current design. Our plans for improving the laser cooling performance are also presented.

To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45/spl deg/ laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2/spl times/10/sup 8/ at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 /spl mu/K, additional transverse cooling even reduces the transverse temperature in one dimension below 30 /spl mu/K. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7/spl times/10/sup -14//spl tau//sup -1/2/. Other applications of continuous beams of cold atoms are suggested.

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