Interaction of a frequency-modulated standing-wave field with a gas subject to magnetic hyperfine splitting

An analysis is made of the influence of the magnetic hyperfine splitting of the methane line at λ = 3.39 ft on the profile of a nonlinear power resonance in the field of a standing frequency-modulated wave. Resonance of this type has been used to stabilize the emission frequency of an He–Ne laser with a methane absorption cell: ^2,3 the frequency reproducibility achieved in this way is ~3×10^–14. The shift of the resonance under investigation is found for different modulation frequencies as a function of the homogeneous width of the transition line and of the standing-wave field intensity.