Frequency Stabilization of the He-Ne Maser

Abstract
A bright and monochromatic radiation from an optical maser can be used as a stable standard of wavelength, when plane mirrors in the maser are automatically controlled so that the oscillation frequency can be kept very close to the center of the atomic line. The separation of mirrors is modulated at a low frequency with a small amplitude. The fundamental-, the second-harmonic, and the third-harmonic components of the modulation frequency in the light output give correction signals for the tilt of mirrors, the power level of excitation, and the separation of mirrors. The photobeat between two independently-stabilized masers of 1.15 microns filled with Ne20 and Ne22, respectively, has been observed. The observed fluctuation of beat frequencies shows a Gaussian distribution, and no systematic frequency drift has been found. It is found that the frequency of each maser stays within several parts in 1010 and the resettability is just as good. Some difficulties with stray magnetic field from magnetostriction coils and with earth magnetic field are found. Preliminary experiments on pressure shift and its effect on the stabilized maser are discussed. The theory has been developed, and the frequency deviations as functions of the gas pressure and of the amplitude of modulation have been calculated.

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