Pressure and Temperature Coefficients of the More Commonly Used Buffer Gases in Rubidium Vapor Frequency Standards

Vapor-cell clock frequency and environmental pressure: Resonance-cell volume changes

“…In the nominal case of N 2 , ∂y/∂P = 560 Hz/torr or in fractional frequency 8.2×10 -8 /torr [10]. Consequently, for a N 2 pressure of 10 torr a fractional volume change of just 10 -4 will produce a fractional-frequency change of 10 -10 .…”

“…Consequently, there will be a temperature change in the clock's physics package elements (i.e., the rf-discharge lamp, the filter cell, and the resonance cell [5]). These temperature changes will, in turn, affect the clock's frequency through a variety of atomic processes: the light-shift effect [6,7] via the lamp's temperature change, the light-shift effect via the filter cell's temperature change, the position-shift effect [8,9] via the resonance cell's temperature change, and the buffer-gas (e.g., N 2 ) shift [10] due to the resonance cell's temperature change. Individually, these atomic processes are reasonably well understood, but how they work together to produce the clock's pressure-shift coefficient is still an area of study.…”

Conversion of laser phase noise to amplitude noise in a resonant atomic vapor: The role of laser linewidth

“…Prior to the present work, this result was completely counterintuitive, as the linewidth of a standard diode laser is roughly 50 MHz [11], while that of a rf-discharge lamp is ~2 GHz [25]. However, in light of the present results, and the fact that optical dephasing rates in gas cell atomic clocks are -100 MHz [26], it can be appreciated that the standard diode laser devices operate in a regime where y~T, the worst possible situation for PM-to-AM conversion noise. Alternatively, PM-to-AM noise is considerably reduced by employing a rf-discharge lamp whose linewidth is much greater than the optical dephasing rate [27].…”

Applications of Vacuum Measurement Technology in China’s Space Programs

“…The use of mixtures of buffer gases, N 2 and Ar for instance, can reduce the temperature coefficient of the absorption bubble to a predetermined value [51]. Therefore, accurate matching and control technique for buffer gases are key techniques for performance enhancement of satellite-borne rubidium atomic clock [52,53]. We have developed a high-precision rubidium atomic clock in LIP, which plays an irreplaceable and decisive role in the construction of China's BeiDou navigation system, as shown in Figure 14.…”