Frequency comparison of iodine-stabilized he-ne lasers at 633 nm from the IMGC and the IFA-IFTAR

The results of an international comparison between the He-Ne lasers stabilized to I-127(2) at 633 nm of the IMGC (Istituto di Metrologia ''G. Colonnetti'', Turin, Italy) and the IFA-IFTAR (Institute of Atomic Physics-IFTAR, Department of Lasers, Bucharest, Romania) are reported. The mean frequency difference, considering the hyperfine structure components d, e, f and g of the R(127)11-5 transition, was Delta nu = nu(RO.2) - nu(IMGC4/5)=3,8 kHz, standard uncertainty u=5,7 kHz, or Delta nu/nu(0)=0,8 x 10(-11), standard uncertainty u=1,2 x 10(-11). The frequency stability, expressed as the relative Allan standard deviation of the beat note between the two lasers, resulted 3,7 x 10(-12) for a 100 s sampling time.