Primary Frequency Standards at NIST

Robert Drullinger

Abstract:	NIST has a more than 50-year history of developing ever more accurate atomic frequency standards. For most of that time, the technology was based on thermal atomic beams of cesium atoms, and the accuracy improvement was approximately a factor of 10 every 7 years. To put this into some kind of perspective, both the period of this history and the rate of improvement are almost identical to the development of information-storage density in magnetic media Now, however, with the advent of laser-cooling schemes and optical- frequency metrology, the rate of progress is dramatically increasing. This paper discusses briefly the last of the thermal-beam standards and our first laser-cooled, atomic-fountain standard. It then goes into some detail about the newly developed all-optical standards that use an optical-frequency transition in a single, laser-cooled, trapped mercury ion or in an ensemble of laser-cooled and trapped calcium atoms. Based largely on the increased operating frequency of the “clock” transition, these new standards have the potential for several orders of magnitude improvement in stability and, in the case of the mercury standard, accuracy over today’s standards operating in the microwave region.
Published in:	Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting November 27 - 27, 2001 Hyatt Regency Long Beach Long Beach, California
Pages:	309 - 320
Cite this article:	Drullinger, Robert, "Primary Frequency Standards at NIST," Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting, Long Beach, California, November 2001, pp. 309-320.
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