Influence of Modulation Frequency in Rubidium Cell Frequency Standards

Alfred Kahan

Abstract:	The error signal which is used to control the frequency of the quartz crystal oscillator of a passive rubidium cell frequency standard is considered. The value of the slope of this signal, for an interrogation frequency close to the atomic transition frequency is calculated and measured for various phase (or frequency) modulation waveforms, and for several values of the modulation frequency. A theoretical analysis is made using a model which applies to a system in which the optical pumping rate, the relaxation rates and the r.f. field are homogeneous. Results are given for sine-wave phase modulation, square-wave frequency modulation and square-wave phase modulation. The influence of the modulation frequency on the slope of the error signal is specified. It is shown that the modulation frequency can be chosen as large as twice the non-saturated full-width at half-maximum without a drastic loss of the sensitivity to an offset of the interrogation frequency from line center, provided that the power saturation factor and the amplitude of modulation are properly adjusted. The interest of square-wave phase modulation is pointed out for large modulation frequencies. Experimental data has been obtained on a laboratory set-up in which a rubidium cell fills a TE microwave cavity. Experimental results achieved with this configuration are in excel lent agreement with the predictions of the given model.
Published in:	Proceedings of the 14th Annual Precise Time and Time Interval Systems and Applications Meeting November 30 - 3, 1982 NASA Goddard Space Flight Center Greenbelt, Maryland
Pages:	85 - 111
Cite this article:	Kahan, Alfred, "Influence of Modulation Frequency in Rubidium Cell Frequency Standards," Proceedings of the 14th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, November 1982, pp. 85-111.
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