Abstract

A means of locking the frequency of a Gunn effect oscillator operating in the 18-26 GHz range, to the spectral line of a molecular gas which exhibits the quadratic Stark effect, has been developed. The gas is confined within a Fabry-Perot semiconfocal cavity resonator at a reduced pressure of the order 1-10 Pa (0.01-0.1 mbar). A sinusoidal Stark voltage of 6 kV peak-to-peak at 4.5 kHz is impressed upon the gas in the cavity which is coupled to the Gunn oscillator operating at a frequency near to the line frequency. The modulation of the spectral line frequency by the Stark voltage electric field generates amplitude modulation of the microwave radiation particularly at the second and fourth harmonics of the Stark voltage frequency. The second harmonic is used to lock the oscillator which is used in a spectrometer for quantitative determinations of the gas used for locking, employing the fourth harmonic. Working with the ammonia 25.056 GHz (J=6, K=6) spectral line, frequency stability of the order +or-30 kHz standard deviation was achieved over the working day.

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