Physics of systematic frequency variations in hydrogen masers

Abstract

The frequency stability of hydrogen masers for intervals longer than 10(4) s is currently limited by systematic processes. The physics of frequency-determining mechanisms internal to the maser that are susceptible to systematic variations, and the connections between these internal mechanisms and external environmental factors are discussed. From estimates of the magnitudes of systematic effects, it is found that the primary internal mechanisms limiting long-term maser frequency stability are cavity pulling, at the level of parts in 10(15) per day, and wall shift variations, at the level of parts in 10(16) to parts in 10(15) per day. Strategies for reducing systematic frequency variations are discussed.

The characterisation of a phase micro-stepper

“…The problem is widespread, and thus probably affects also other types of the phase micro-steppers such as the AOG. The phase-matched cables are also important for the frequency stability of the active hydrogen masers [15]. The phase-matching of cables is analogous to optical anti-reflection layers that are common in today's optics, but it is not common in the radiofrequency applications.…”