The physics of the environmental sensitivity of rubidium gas cell atomic frequency standards

The physical mechanisms behind environmental sensitivity are considered, and they are related to the performances of rubidium frequency standards (RFSs). Some of the RFS environmental sensitivities are due to simple physical mechanisms like the effect of DC magnetic field on the Rb hyperfine resonance frequency. For these, an analysis can be based on physical principles and straightforward design factors. Other environmental factors, like temperature sensitivity, are more complex combinations of many effects, both physical and practical, and the analysis often takes the form of an error budget, with large unit-to-unit variations. Today's RFSs span a wide performance range from small, inexpensive units with pp10(10) error budgets to larger, higher-performance versions offering pp10(14) stabilities. For both extremes, however, environmental sensitivity can be the most significant performance limitation. Why this is the case is explained, and some insight into how to make improvements is offered.