Stabilization of the He–Ne Maser on the Atomic Line Center

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Abstract
Application of an automatic feedback control for long‐term frequency stabilization of a He–Ne optical maser at the center frequency of the atomic resonance is described. The length of the Fabry‐Perot resonator is modulated at a low frequency with small amplitude. The fundamental, second harmonic, and third harmonic components of this modulation frequency in the light output of the maser are used to control the tilt angles of the mirrors, the radio‐frequency excitation power input, and the separation of the mirrors, respectively. The frequency stability is determined by observing the photobeat between the outputs of two independently stabilized masers. Isotopically enriched samples of Ne are used in the two masers with one of them enriched in 20Ne and the other in 22Ne. The optical output of a maser stabilized in this manner is frequency modulated and the center frequency has been found to be stable to several parts in 1010 over very long periods.

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