Accuracy of the computer controlled laser frequency standards based on resolved hyperfine structure of a methane line

We present 2-years results of frequency comparisons of the transportable He-Ne laser standards at 3.99 /spl mu/m stabilized to components of magnetic hyperfine structure (MHFS) of F/sub 2//sup (2/)-line of methane, and stationary laser using resolved recoil doublet. Absolute frequency measurements of the transportable laser have been made and this value was transferred to the stationary one. On the basis of theoretical model of the line shape the frequency of unperturbed transition have been calculated.<
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