Accurate frequency measurements in the infrared using stabilized CO2/OsO4 lasers

A new calibration of an OsO4 absolute frequency grid is reported with an uncertainty less than 100 Hz in the 28/29 THz range (delta nu/nu similar to 3 x 10(-12)). A precedent determination has been performed fifteen years before, with uncertainties ranging from 50 Hz to 2 kHz. These OsO4 transitions confer high metrological performances to CO2 lasers when frequency locked on the third harmonic of the saturated resonances. We report also recent results on the stability of the BNM-LPTF CO2/OsO4 optical frequency standard in term of short-term stability of 3 x 10(-14) tau(-1/2) and long term stability of 2.4 x 10(-15) for 3 000 s of integration time. This result corresponds, to our knowledge, to the best stability achieved, up to now, in the optical domain.