Power shift of the frequency of an He–Ne–CH4 laser

An experimental investigation was made of the dependence of the frequency shift of a stabilized He–Ne–CH₄ laser on the degree of saturation of an absorbing medium and on its gas pressure. When the saturation parameter I_8,7[0] was increased from 0 to 1, the emission line, whose homogeneous width was 75 kHz, shifted by 400 ± 40 Hz. The dependence of the shift on the saturation parameter was nonlinear. A theoretical calculation was made of the shift of the frequency at the tip of the dip which appeared in the absorption line due to the magnetic hyperfine structure of the molecular transition.