Determination of CO2/SF6 metrological characteristics with a femtosecond laser system: 1 Hz reproducibility at 10 μm

A new standard is currently being developed in the 30 THz region, using SF₆ two-photon Ramsey fringes as a reference. A standard in this region is important for several reasons: molecular spectroscopy, fundamental measurements on molecular systems such as tests of the violation of parity or the Pauli principle in molecules, and temporal variation of the fundamental constants. A new system has implemented consisting of a femtosecond laser system for frequency measurement which allows direct measurement and control of the absolute frequency of the CO₂laser. The reference frequency is provided by a 100 MHz signal controlled by the H-maser and the Cs fountain of the BNM-SYRTE in Paris, and transmitted to the laboratory through an optical fibre. The whole system can be used for spectroscopic purposes, here measuring the SF₆ transition, with an improved long term stability of the reference laser via the femtosecond system.