Frequency-modulation resonances in He–Ne/CH4 lasers and their use for frequency stabilization

The results are given of theoretical and experimental investigations of frequency-modulation saturated-absorption and saturated-dispersion resonances in a linear He–Ne laser employing an intracavity methane absorption cell. The ultimate sensitivity of the method of frequency-modulation spectroscopy of an intracavity absorbing gas was shown to be 10^–11cm^–1·Hz^1/2. Studies were made of the stability and of the frequency shifts of a linear He–Ne/CH₄ laser stabilized by frequency-modulation resonances of the saturated dispersion and saturated absorption. A frequency stability of 8×10^–15 for an averaging time of 1 sec and a frequency reproducibility of 10^–13 were obtained.