The Optically Pumped Rubidium Vapor Frequency Standard

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 10
⁸
and with a signal-to-noise ratio, in a one-second noise bandwidth, in excess of 10
⁴
. 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.