Method of extraction of hyperfine structure influence on methane line (lambda=3.39 mu m) used in optical frequency standards

We have shown that the triplet line of methane (lambda = 3.39 mum) at arbit rary saturation can be described with an accuracy of 1-2% as a sum of three resonances with the same shape and relative intensities 6:7:8. This statem ent was proved in general form without any assumptions about the real line shape and mechanisms of broadening and is valid for any method of resonance registration (saturation absorption, saturation dispersion, Ramsey resonan ces). That permitted us by use of Fourier transforms and the pre-knowledge about frequency distances between these hyperfine components to suggest the method of extracting of single line from the spectrogram of overlapping co mponents of the hyperfine structure without any additional supposing about a form of resonance. This method also has internal possibilities to define these distances. It takes off the problem of uncertainty of the methane fre quency standard caused by hyperfine structure. (C) 2000 Published by Elsevi er Science B.V.