The performance of an ammonia maser with two resonators in cascade

An ammonia maser is described in which an additional resonant structure is inserted between the microwave cavity and the electrostatic separator. Observation of the power level of the microwave oscillation is shown to be a sensitive means of detecting various types of molecular transitions in the auxiliary resonator. It is found that when this auxiliary resonator is a microwave cavity which can be tuned across the molecular resonance, the power level of the oscillation in the maser cavity varies in a more complex way than would be expected on consideration of population differences alone. In particular, a beat signal of frequency 4-5 kc/s superimposed on the normal oscillation signal is observed for a critical detuning of the additional cavity from the molecular resonance frequency. The case when the auxiliary cavity takes the form of a multimode ultramicrowave resonator is also considered. It is suggested that transitions of ammonia molecules amongst the various rotational levels should be observable through changes in the amplitude of microwave oscillation.