Measure Journal Volume 2 Article 34 NCSL International

NIST Primary Frequency Standards and the Realization of the SI Second

NCSLI Measure | Vol. 2 No. 4 (2007) | https://doi.org/10.1080/19315775.2007.11721402
Publisher NCSL International | Published December 2007 | pp. 74-89

Abstract Authors References Article PDF Citation(s)

Abstract

As the base unit of time interval, the second holds a place of preeminence in the world of metrology. Time interval, and its reciprocal, frequency, can be measured with more resolution and less uncertainty than any of the other physical quantities. The precise realization of the second was made possible by the development of frequency standards based on the energy transitions of atoms, an event that not only revolutionized the science of timekeeping, but also forever changed many other areas of metrology. The definitions of other units in the international system (SI), including the meter, candela, ampere, and volt, now depend upon the definition of the second. In the approximate half century since atomic frequency standards were first introduced, the progress in time and frequency metrology has been rapid and relentless. Today, the National Institute of Standards and Technology (NIST), maintains the world's most accurate primary frequency standard, a laser-cooled cesium fountain known as NIST-F1. Since its completion in 1998, NIST-F1 has been continuously improved and is currently accurate to within 4 × 10−16. NIST-F2, a second-generation atomic fountain standard now being built, promises even better accuracy. This paper explores both the history and the technology of NIST primary frequency standards, beginning in the pre-atomic era and continuing through the present day.

(Print: ISSN 1931-5775) (Online: ISSN 2381-0580)
©2007 NCSL International

Authors

Michael A. Lombardi 0000-0001-8027-034X

Time and Frequency Division
National Institute of Standards and Technology
Boulder, CO

Thomas P. Heavner

Time and Frequency Division
National Institute of Standards and Technology
Boulder, CO

Steven R. Jefferts

Time and Frequency Division
National Institute of Standards and Technology
Boulder, CO

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Citation(s)

M. Lombardi, "NIST Primary Frequency Standards and the Realization of the SI Second," NCSLI Measure, Vol. 2 No. 4, pp. 74-89, https://doi.org/10.1080/19315775.2007.11721402

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Vol. 2 No. 1 (2007)
Vol. 2 No. 2 (2007)
Vol. 2 No. 3 (2007)
Vol. 2 No. 4 (2007)