Light and Buffer-Gas Frequency Shifts in the 85Rb-Maser Frequency Standard

Recently we reported the operation of an optically pumped 85Rb maser oscillating at 3.035734 GHz on the field-independent transition 52S1/2(F = 3, mF = 0 → F = 2, mF = 0) [1]. Apart from cavity pulling, the two major sources of frequency shifts are those due to the buffer gas and the pumping light. The short-term phase stability of the standard is not appreciably affected by these shifts. The buffer-gas shift can be used to advantage to select an output frequency that is different from the ground-state hyperfine frequency.