Frequency of a methane-stabilized helium-neon laser

A phase-locked laser frequency chain was used to measure the absolute frequency of a HeNe/CH/sub 4/ laser relative to the primary Cs standard, with measurement uncertainty less than +or-1 part in 10/sup 12/. The frequency depends on laser parameters; a spread of 8.3*10/sup -11/ was observed. This was attributed to the variation of Lamb dip asymmetry resulting from the gas-lens effect and the accompanying diffraction loss variation near resonance. Means of improving laser frequency reproducibility by reducing cavity diffraction loss variation were studied experimentally. The frequency obtained with a cavity exhibiting the smallest Lamb dip asymmetry was found to be 88 376 181 599.07+or-0.07 kHz.>