Frequency measurements of saturated-fluorescence-stabilized CO2 laser lines:: comparison with an OsO4-stabilized CO2 laser standard

We have used the Villetaneuse saturated absorption spectrometer working in the 10 mu m region, referenced to the OsO4 frequency grid, to test the performance of the saturated fluorescence method for CO2 laser frequency stabilization. The Allan variance for the saturated-fluorescence-stabilized CO2 laser reached 60 Hz for an integration time of 300 s. We also performed three absolute measurements of CO2 laser frequencies stabilized by the saturated fluorescence method, with a sub-kHz accuracy. We obtained a 1.7 kHz redshift of the CO2 saturated fluorescence lines, which we attribute essentially to pressure. This is in contradiction with the previous observation of a blueshift [K.L. SooHoo, C, Freed, J.E. Thomas, H.A. Haus: Phys. Rev. Lett. 53, 1437 (1984)]. Furthermore, significant deviations of the measured frequencies from the data of Maki et al. [A.G. Maki, C.-C. Chou, K. Evenson, L.R. Zink, J.T. Shy: J. Mel. Spec. 167, 211 (1994)] demonstrate the need for a new calibration of the CO2 frequency grid.