CO2-LASER STABILIZED ON NARROW SATURATED ABSORPTION RESONANCES OF CO2- IMPROVED ABSOLUTE FREQUENCY MEASUREMENTS

We have stabilized a CO2 laser on narrow saturated absorption resonanc es of CO2 detected on the transmitted beam of an external Fabry-Perot cavity in the 30 THz spectral region. By using another CO2 laser stabi lized on a close OsO4 line whose absolute frequency is precisely known , and measuring the beat frequency with a precision of 100 Hz, we dete rmined the absolute frequency of twenty CO2 laser lines, with uncertai nties between 100 Hz and 1 kHz mainly limited by the accuracy of the O sO4 grid. This set of measurements reveals some discrepancies with dat a based on measurements performed with the widely used saturated fluor escence technique; we attribute these to pressure shifts of several ki lohertz under the conditions of this last method.