The Proton Magnetic Resonance Oscillator, a Radio Frequency Source of High Spectral Purity

Some basic properties of a proton maser making use of the dynamic Overhauser effect for population inversion and enhancement are reviewed. The long proton spin relaxation times of liquid samples, in the order of seconds, facilitate the production of self-sustained continuous oscillation with high spectral purity. Theoretically the proton maser oscillator should have a spectral purity of some parts in 10¹⁴ for an inhomogeneously broadened proton resonance absorption linewidth of 100 cps at a frequency of 15 Mc. A proton maser was operated at this frequency in a temperature stabilized permanent magnet. In preliminary experiments a frequency drift in the order of 1 part in 10⁹/sec was measured. The spectral purity was tested by beating together the frequencies of two proton maser oscillators operating within the same magnetic field. Preliminary results yielded frequency deviations of less than 6 parts in 10¹⁰. The sources introducing frequency instability are discussed and their relative contributions evaluated.