International comparisons of He-Ne lasers stabilized with¹²⁷I₂at = 633 nm (July 1993 to September 1995). Part II: Second comparison of Northern European lasers at = 633 nm

Abstract

This second Northern European comparison between seven lasers exhibits closer results than the first comparison. A standard uncertainty of 5 kHz was obtained against 15 kHz in 1990, while the frequency average of the group of lasers was about the same with 3,9 kHz, using the BIPM4 laser as reference. A large frequency difference on a laser observed during the first comparison was again observed; partial explanations of the origin of this difference were found. This difference has been excluded from the calculation of the average. Typical frequency stabilities using Allan standard deviations of about 1,6 × 10-11 and 1,7 × 10-12 were observed on 1s and 100 s sampling times, respectively.