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

For space-qualified vapor-cell atomic clocks, the pressure-shift coefficient describes the frequency change as the device transitions from atmospheric pressure to vacuum. Two processes are known to affect this frequency change: a thermal pathways mechanism and a resonance-cell volume mechanism (i.e., the so-called barometric frequency shift). Here, we focus on the barometric frequency shift, and employ finite element methods to examine how the barometric shift depends on resonance-cell size and wall thickness.