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NIST Cesium Fountains – Current Status and Future Prospects



Steven R. Jefferts, Thomas P. Heavner, Thomas E. Parker, Jon H. Shirley


We review the current status of the U.S. Primary Frequency Standard, NIST-F1. NIST-F1 is a laser-cooled cesium fountain based frequency standard with an inaccuracy of less than δ f/f {less than or equal to} 5×10-16 limited mainly by the radiation field in the room-temperature fountain (blackbody shift). NIST-F1 is one of the best cesium fountain currently contributing to international atomic time, but has reached a point that it is impractical to improve its accuracy substantially. Therefore we are building a new fountain, imaginatively named NIST-F2, with a cryogenic (77K) Ramsey interrogation zone which lowers the blackbody shift by several orders of magnitude. NIST-F2 is currently undergoing final assembly and we will discuss our planned (hoped for) performance which includes frequency inaccuracy of δ f/f {less than} 1×10^-16^.
Proceedings of the SPIE: Time and Frequency Metrology


atomic clock, cesium clock, primary frequency standard


Jefferts, S. , Heavner, T. , Parker, T. and Shirley, J. (2007), NIST Cesium Fountains – Current Status and Future Prospects, Proceedings of the SPIE: Time and Frequency Metrology, [online], (Accessed June 25, 2024)


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Created September 12, 2007, Updated February 17, 2017