Steady-state noble gas Zeeman masers operating with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ have been realized by spin exchange with laser optically pumped Rb. These masers can operate continuously for arbitrary lengths of time. For measurement intervals τ=1000 to 10 000 s, frequency measurement precision for a phase locked ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ maser is shown to be better than 1×${10}^{\mathrm{-}2}$${\mathrm{\tau }}^{\mathrm{-}3/2}$ Hz. Startup transients are used to study gain characteristics. In a two-cell setup maser conditions for both species can be optimized allowing a wide array of precision measurements.

• Received 15 November 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.2363