Results of international comparisons using methane-stabilized He-Ne lasers at 3.39 μm and iodine-stabilized He-Ne lasers at 633 nm

The results of international comparisons of methane-stabilized He-Ne lasers at λ = 3.39 μm and iodine-stabilized He-Ne lasers at 633 nm, made by beat frequency techniques, between Bureau International des Poids et Mesures (BIPM) and eleven national laboratories are presented. Generally, the measured frequency differences were inside /spl I.chemo/4 × 10^-11; but greater frequency differences were observed with some iodine cells (probably as a result of contamination) or when the output power of one laser was two or three times greater than the power of the other laser.