NIST Cesium Fountains – Current Status and Future Prospects

Published

September 12, 2007

Author(s)

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

Abstract

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^.

Citation

Proceedings of the SPIE: Time and Frequency Metrology

Volume

6673

Issue

667309

Pub Type

Journals

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Keywords

atomic clock, cesium clock, primary frequency standard

Citation

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], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50590 (Accessed October 8, 2025)