Comparison of Theoretical and Observed Hydrogen Maser Stability Limitation due to Thermal Noise and the Prospect for Improvement by Low-Temperature Operation.

摘要

Expressions describing the limitations to hydrogen maser stability due to random thermal noise are derived in terms of parameters that govern the operation of the maser oscillator. Possible effects from cavity pulling have been included by the ad hoc assumption of a random cavity resonance frequency variation characterized by a 1/f spectrum. The measured stability of the recently developed SAO VLG-11 masers is compared with the predicted stability limitations, and good agreement with theory is found for averaging times tau between 0.83 sec and 4200 sec. The best observed Allan variance is sigma (2, 4200, 4200, 6) = 6 x 10 to the -16th power. For tau > 4200 sec systematic variations appear to dominate the data, and the variance representation is no longer appropriate. Using the stability limitation expressions the consequences of low temperature maser operation is analyzed. If the wall relaxation probability per collision remains at or below its room temperature value, there is a high likelihood of substantial improvement in maser performance from operation at cryogenic temperatures.