Zeeman effects in gaseous He-Ne optical masers

In this paper, experimental and theoretical results of a detailed study of the Zeeman effects in a gaseous He-Ne optical maser under weak and normal excitation conditions are given. Attention is confined to the strongest maser emission line (2s2→2p4). Under weak excitation conditions, the maser emission is a doublet of right and left circularly polarized waves. These may belong to either the same cavity mode or different cavity modes, depending on the strength of the applied magnetic field. When viewed through a linear polarizer, the maser emission is amplitude modulated. Under normal excitation conditions, for suitable magnetic fields, the maser could oscillate in at least three modes. The maser emission would then consist of a pair of right circularly polarized waves of two different cavity resonant frequencies and a pair of left circularly polarized waves of different frequencies. In this case, a beat note at the difference frequency is photo-detected without the need for a linear polarizer. An interesting phase relationship among the various components of the maser multiplet is found. This phase relationship can be explained when the nonlinearity due to saturation is taken into account.