Long-Term Frequency Stability of the Rb87 Maser

A description of a compact Rb87 maser approximately 20 cm in diameter and 30 cm in length is given and the features of the principal components are discussed. The fractional frequency fluctuations (Allan variance) are less than 5 × 10-13 for averaging times between 1 and 103 s. The effects of various parameters on the maser frequency are investigated experimentally and compared to theoretical predictions obtained from the maser frequency equation.