Metrological properties of CO2/OsO4 optical frequency standard

Recent progress on the metrological performance of the BNM-LPTF CO2/OsO4 frequency standards in the 28/29 THz range, using OsO4 molecular transitions as a frequency reference is reported. Significant improvements in terms of both short-term stability (6.6 x 10(-14)/root tau up to tau = 300 s) and long-term stability (4 x 10(-15) up to tau = 1000 s, Delta nu v similar to 0.1 Hz) are obtained. Long term reproducibility (over more than 18 months) of about 3 x 10(-13) has been achieved. This high level enables the transfer, in terms of absolute frequency at the 3 x 10(-13) level of uncertainty, from primary frequency standards in the microwave domain to near infrared and visible domains, using frequency chains with CO2/OsO4 as a transfer frequency standard. Preliminary estimates of the main effects which may shift the OsO4 center line are reported.