Analysis of Fundamental and Systematic Effects Limiting Hydrogen Maser Frequency Stability

The hydrogen maser is currently one of the most stable frequency standards currently available, providing frequency stabilities of several parts in 1 0 ' for averaging times of lo3 lo4 seconds. Further improvement to the stability of hydrogen masers requires a comprehensive understanding of the relative magnitudes of physical processes that influence frequency stability. We discuss an approach to understanding a variety of thermodynamic and systematic processes that can affect maser frequency stability.['] This examination enables the maser researcher and user to identify stability-limiting effects and thus to choose areas where improvements could lead to increased stability. As is true with many complex systems, overall improvements can generally be gained only by attending simultaneously to a variety of factors. Improving one aspect of the maser will not significantly increase the frequency stability if variations in another area limits the stability to a level comparable to the first.