LOCAL OSCILLATOR INDUCED DEGRADATION OF MEDIUM-TERM STABILITY IN PASSIVE ATOMIC FREQUENCY STANDARDS

G.J. Dick, J.D. Prestage, C.A. Greenhall, L. Maleki

Abstract:	As the performance of passive atomic frequency standards improves, a new limitation is encountered due to frequency fluctuations in an ancillary local oscillator (L.O.). The effect is due to time variation in the gain of the feedback which compensates L.O. frequency fluctuations. The high performance promised by new microwave and optical trapped ion standards may be severely compromised by this effect, He present an analysis of this performance limitation for the case of sequentially interrogated standards. The time dependence of the sensitivity of the interrogation process to L.0, frequency fluctuations is evaluated for single-pulse and double-pulse "Ramsey" RF interrogation and also for amplitude modulated pulses. The effect of these various time dependencies on performance of the standard is calculated for an L.O., with frequency fluctuations showing a typical 1/f spectral density. A limiting 1/VT dependent deviation of frequency fluctuations is calculated as a function of pulse lengths, dead time, and pulse overlap. He also present conceptual and hardware-oriented solutions to this problem which achieve a much more nearly constant sensitivity to Lo. fluctuations. Solutions involve: use of double-pulse interrogation; alternate interrogation of multiple traps so that the "dead time" of one trap can be covered by operation of the other; and the use of double-pulse interrogation for two traps, so that during the time of the RF pulses, the increasing sensitivity of one trap tends to compensate for the decreasing sensitivity of the other. A solution making use of amplitude-modulated pulses is also presented which shows nominally zero time variation.
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:	487 - 508
Cite this article:	Dick, G.J., Prestage, J.D., Greenhall, C.A., Maleki, L., "LOCAL OSCILLATOR INDUCED DEGRADATION OF MEDIUM-TERM STABILITY IN PASSIVE ATOMIC FREQUENCY STANDARDS," Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting, Vienna, Virginia, December 1990, pp. 487-508.
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