Abstract
The results of an international comparison of iodine-stabilized He-Ne lasers at 633 nm, made by beat-frequency techniques, between the NRLM (Japan) and the BIPM are presented. During two weeks the frequency of the two lasers NRLM1 and BIPM4 were compared twice a day. The mean frequency difference was determined to be Δf = [0.9 ± 2.6] kHz, corresponding to a relative frequency difference of [2 ± 5] 10-12. Parameters which affected the frequency of the lasers such as modulation width, iodine pressure and laser power were also investigated. As the laser BIPM4 was compared with the laser BIPM2 at the BIPM before and after the travel to the NRLM, we can link our results to the previous international comparisons in which the BIPM has participated.