THE PHYSICS OF THE ENVIRONMENTAL SENSITIVITY OF RUBIDIUM GAS CELL ATOMIC FREQUENCY STANDARDS

W.J. Riley

Abstract:	Environmental sensitivity is often the most significant limitation to the practical stability of rubidium frequency standards (RFS). For example, temperature sensitivity can cause a rapid frequency change of several parts in 101" for a tactical RFS that has an aging of only Ix10-11 (month. Other important environmental factors are barometric pressure, vibration, magnetic field, and nuckar radiation. This paper considers the physical mechanisms that lie behind these environmental sensitivities, and relates them to the performance of actual rubidium frequency standards. It is part of an effort currently underway under NIST and IEEE sponsorship toward a standard characterizing such environmental sensitivities. For the systems designer, a better understanding of the reasons for RFS environmental sensitivity will help in making program tradeoffs. For the user of these devices, a better knowledge of the causes for Rb clock instability will aid in their testing and proper application. For the time and frequency specialist, a review of these factors may prove useful toward improving RFS design. Some of the RFS environmental sensitivities are due to simple physical mechanisms like the effect of de magnetic field on the Rb hyperfine resonance frequency. For these, an analysis can be based on physical principles and straightforward design factors. Other environmental factors, like temperature sensitivity, are more complex combinations of many effects, both physical and practical, and the analysis often takes the form of an error budget with large unit-to-unit variations. Today's rubidium frequency standards span a wide performance range from small, inexpensive units with pp10^10 error budgets to larger, higher performance versions offering pp10^14 stabilities. For both extremes, however, environmental sensitivity can be the most significant performance limitation. This paper helps explain why, and offers some insight into how to make improvements.
Published in:	Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting December 4 - 6, 1990 Sheraton Premiere Hotel Vienna, Virginia
Pages:	441 - 452
Cite this article:	Riley, W.J., "THE PHYSICS OF THE ENVIRONMENTAL SENSITIVITY OF RUBIDIUM GAS CELL ATOMIC FREQUENCY STANDARDS," Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting, Vienna, Virginia, December 1990, pp. 441-452.
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