Nonlinear resonances of natural intensity fluctuations in a two-mode He–Ne/CH4 laser

The influence of a nonlinear absorber (methane) on the natural intensity fluctuations in an He–Ne laser (λ = 3.39 μm) emitting two linearly and orthogonally polarized modes with a controlled intermode interaction was studied experimentally and theoretically for the first time. It was found that an intracavity methane cell increases appreciably the influence of the fluctuation sources on the natural intensity fluctuations.