Transportable He-Ne/CH/sub 4/ optical frequency standard and absolute measurements of its frequency

A new version of a transportable double-mode He-Ne/CH/sub 4/ laser (3.39 /spl mu/m) stabilized on the resolved hyperfine structure (HFS) of the F/sub 2//sup (2/) methane line was designed at Lebedev Physical Institute. Absolute frequency measurements of the laser were made at the radio-optical frequency chain of Physikalisch-Technische Bundesanstalt, Braunschweig, Germany (PTB). Various reasons for frequency shifts were investigated. Computer processing of the observed line shape was used to calculate the nonperturbed frequency of the central component of HFS.