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A study of coherence phenomena in an ammonia maser

Bardo, William Stanley

A study of coherence phenomena in an ammonia maser Thumbnail


William Stanley Bardo


The design and operation of an advanced ammonia beam maser is described. Special features of the design permit operation of the device as an oscillator without the benefit of pumping with liquid nitrogen. Further, one novel feature allows variation of the beam geometry, while the system is under vacuum, to suit different conditions of operation. By virtue of these developments the device has a relatively high efficiency compared with other ammonia masers when it is operated with liquid nitrogen pumping.
The investigations described here are part of a wider exploration of the analogies that exist between.various electric dipole and. magnetic dipole systems. In particular, it has proved possible to produce two effects for which theory suggests a very small chance of occurrence in an ammonia maser: the transient that follows switching on (and off) of the oscillation; and the oscillation pulsations (spiking) consequent upon periodic modulation of the oscillation condition. These are familiar adjuncts of laser and maser action in many solid-state systems.
A second resonant microwave cavity is employed to monitor the effects on the beam of coherent transitions occurring in the first cavity for a range of beam intensities. The change in relative populations between the two levels is followed by operating the second cavity in the spectroscopic mode, and looking for absorption or stimulated emission in the beam. A complementary study of the polarisation imparted to the beam by the first cavity is made by observing the change in oscillation level within the second cavity as a function of the frequency detuning of the first resonator. The relationship between the spectroscopic observations and the polarisation effects is clarified in a general treatment for the detuning phenomena. Predictions are made for new types of detuning phenomena, and sane tentative support is offered for these predictions.
The analysis of the partial saturation behaviour in the first cavity leads to a proposal for a method of producing a beam composed predominantly of relatively slow molecules. The technique is general in scope and is not restricted to maser media. It offers possibilities of application in frequency standards and in high resolution gas spectroscopy.

Publication Date Nov 1, 1969


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