International comparison of He-Ne lasers stabilized with ¹²⁷I₂ at λ ≈ 543 nm (December 1999)

This second international comparison between He-Ne lasers at 543 nm exhibits similar results to the first international comparison. A standard uncertainty of 4 kHz was obtained against 2 kHz in 1993, while the average frequency difference between the lasers was -1.0 kHz against 14.2 kHz in 1993. The experimental data indicate however that a standard uncertainty below 1 kHz can be expected between two lasers. The frequency difference between the two lasers clearly lies within the limits (2.5 parts in 10¹¹) given in the revised practical realization of the definition of the metre (1997) for the 633 nm He-Ne laser.