A Model of the Separated Filter Cell Rb Atomic Clock

The separated filter cell rubidium (Rb) atomic clock finds application in much of modern technology’s infrastructure due to its small size, weight and power (SWaP), its reliability and longevity, and its ability to achieve high levels of frequency stability over long averaging times. Technology areas where the Rb clock finds application range from 5G communications to satellite navigation systems. Here, we expand on previous work to provide a model of the vapor cell clock that includes the full set of clock physics package elements: the rf-discharge lamp’s emission, the spectral modification of the lamplight by the filter cell, and the optical pumping efficiency of the lamplight in the clock’s resonance cell. Additionally, the model now includes spatial variations in the light-shift, the quadratic Zeeman shift, the spin-exchange shift and the temperature-gradient shift in the resonance cell. This model allows the researcher/engineer to examine (for example) the influence of filter-cell temperature or resonance-cell buffer-gas composition on the clock’s signal-to-noise ratio and sensitivity to environmental perturbations. This new model will aid in the design of next-generation vapor-cell clocks with reduced SWaP and will also be useful in training AI protocols meant to diagnose anomalous on-orbit clock behavior.