Single-mode collapse in 6328-Å He–Ne lasers

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Abstract
Internal-mirror 6328-Å He–Ne lasers have an intramode frequency difference when placed in a transverse magnetic field. When the magnetic field strength is increased until the Zeeman frequency shift approaches the mode spacing, mode coupling is induced. In some multimode lasers, this mode coupling results in a collapse into single-mode operation with no loss of over-all laser power in the output. The intramode frequency difference can be exploited to produce a simple frequency stabilization system whose frequency variation is less than 1 part in 1010. Plots of beat frequency variation and single-mode tuning range are included.