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

Laser-cooled microgravity clocks

Chad Fertig, Kurt Gibble, Bruno Edson Klipstein, James M. Kohel, L. Maleki, David J. Seidel, R. Thompson

Published Jan 22, 2003• 2 citations
Publisher

Abstract

Designs for planned space clock missions are described. The cold collision shift and multiple launching (juggling) have important implications for the design and the resulting clock accuracy and stability. In a recent fountain experiment, we have demonstrated some of the trapping and cooling techniques for our design of a microgravity clock.

DOI
10.1109/freq.1999.840729

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Limitations to the performance of laser-cooled earth and space-based Cs clocks will be critically discussed. The most significant limitation to the stability and accuracy of laser-cooled atomic clocks is the frequency shift due to cold collisions. Because of it, laser-cooled Cs clocks must be operated at low density and this implies that space based Cs clock performance will not be significantly better than earth based. To regain some of the high accuracy and stability lost to the low density, clocks can be designed to multiply launch (or juggle) atoms. Clocks based on other atoms, in particular Rb-87 or possibly Rb-85, may have much smaller cold collision frequency shifts and therefore be capable of higher stability and accuracy, especially in a space environment.

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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•Nov 8, 2002•8 citations
Designs for planned space clock missions are described. The cold collision shift and multiple launching (juggling) have important implications for the design and the resulting clock accuracy and stability. In a recent fountain experiment, we have demonstrated some of the trapping and cooling techniques for our design of a microgravity clock.
The principle advantage of microgravity for atomic clocks is interrogation times longer than 1 s. With a 10 s interrogation time, a clock has a 50 mHz linewidth suggesting that accuracies may potentially exceed 10/sup -16/. However, to achieve greater accuracy within the same averaging time, greater stability is needed. Achieving greater stability in a microgravity clock constrains the design differently than for earth based fountains. In this paper, we discuss the design considerations for laser-cooled microgravity clocks highlighting the considerations that differ from those for earth-based fountains. As in earthbased fountains, the frequency shift due to cold collisions plays an important role in the design of the clock. Given our predictions (and measurements) for the shift in laser-cooled Rb clocks, we currently anticipate building a high performance Rb clock and discuss the relative merits of Rb and Cs microgravity clocks. Finally, we present our tentative designs for two microgravity clocks.
Limitations to the performance of laser-cooled earth and space-based Cs clocks will be critically discussed. The most significant limitation to the stability and accuracy of laser-cooled atomic clocks is the frequency shift due to cold collisions. Because of it, laser-cooled Cs clocks must be operated at low density and this implies that space based Cs clock performance will not be significantly better than earth based. To regain some of the high accuracy and stability lost to the low density, clocks can be designed to multiply launch (or juggle) atoms. Clocks based on other atoms, in particular Rb-87 or possibly Rb-85, may have much smaller cold collision frequency shifts and therefore be capable of higher stability and accuracy, especially in a space environment.