Frequency stability and reproducibility of the 3.39 μm He−Ne laser stabilized on the methane line

Physical factors determining the frequency reproducibility of a gas laser with nonlinear absorption are analyzed. On the basis of experimental and theoretical results it is shown that the collisional shift, the second-order Doppler effect, the recoil effect, and the magnetic hyperfine structure do not reprsent the limitation in achieving a frequency reproducibility of the order of 10^?13?10^?14. This paper reports on experiments achieving frequency stability of 5·10^?15 and reproducibility of 3·10^?14 for the 3.39 μm He?Ne laser with an internal methane cell.