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

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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. Mol. Spec. 167, 211 (1994)] demonstrate the need for a new calibration of the CO₂ frequency grid.