International comparison of He-Ne lasers stabilized with I-127(2) at lambda approximate to 543 nm (December 1999) - Northern European lasers

This second international comparison between He-Ne lasers at 543 nm exhibit s similar results to the first international comparison. A standard uncerta inty of 4 kHz was obtained against 2 kHz in 1993, while the average frequen cy difference between the lasers was -1.0 kHz against 14.2 IcHz in 1993. Th e experimental data indicate however that a standard uncertainty below 1 Ic Hz can be expected between two lasers. The frequency difference between the two lasers clearly lies within the limits (2.5 parts in 10(11)) given in t he revised practical realization of the definition of the metre (1997) for the 633 nm He-Ne laser.