Investigation of frequency resonance of a saturated methane transition in He–Ne/CH4 laser radiation with modulation of the resonator length

An experimental investigation was made of frequency resonances in the frequency deviation of He–Ne/CH₄ laser radiation under conditions of modulation of the resonator length. Changes in the profile and contrast of these resonances were studied as a function of the modulation frequency. It was found that at low modulation frequencies the effects observed are due to saturation of the dispersion, whereas at high modulation frequencies (compared with the methane line width) these effects are due to saturation of both the dispersion and of the absorption of the methane lasing transition.