The Optically Pumped Rubidium Vapor Frequency Standard

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Abstract
Recent work on gas cell frequency standards has led to a clearer understanding of the capabilities of such systems. The physics of the quantum mechanical system allows the designer to start with a linewidth of approximately 1 part in 108 and with a signal-to-noise ratio, in a one-second noise bandwidth, in excess of 104. Carefully engineered systems have been demonstrated to have high stability with high reliability and small weight and volume. Frequency stability, which is the important quality of a standard, has been studied over a wide range of averaging and measurement times. A plot of standard deviation of frequency stability σ shows a broad minimum of σ= 2.5×10-12 for a run of 40 hours; a σ= 2×10-11 for a run of 15 minutes (¼ second averaging time); and σ = 4×10-11 for a run of 330 days.