International comparisons of He-Ne lasers stabilized with I-127(2) at lambda approximate to 633 nm - Part VII: Comparison of NORAMET I-127(2)-stabilized He-Ne lasers at lambda approximate to 633 nm

This paper reports the seventh set of results of a series of grouped laser comparisons from national laboratories undertaken by the Bureau Internation al des Poids et Mesures (BIPM) at the request of the Comite Consultatif pou r la Definition du Metre (CCDM, now the Consultative Committee for Length, CCL), during the periods July 1993 to September 1995 and March to July 1997 . The results of this comparison, involving six lasers from three countries o f North America and from the BIPM, meet the goals set by the CCDM in 1992 a nd adopted by the Comite International des Poids et Mesures (CIPM) the same year. The standard uncertainty (1 sigma) of the frequency of the He-Ne las er stabilized on the saturated absorption of I-127(2) at lambda approximate to 633 nm is reduced to a level of 12 kHz (2.5 x 10(-11)) when the lasers compared meet the recommended values of the parameters. The lasers were first compared with the BIPMP3 laser, with all the lasers s et to the parameter values normally used in each laboratory; the results th en ranged from -10.1 kHz to 19.0 kHz. After checking and correcting the val ues of all the parameters, the range was reduced to -10.6 kHz to +2.6 kHz. Under the latter conditions, the average frequency difference of the group of lasers, with respect to the BIPM4 laser, was +0.3 kHz with a standard un certainty (1 sigma) of 5.3 kHz. The best relative frequency stabilities, wi th Allan standard deviations of about 6.2 x 10(-12), 5.1 x 10(-13) and 1.4 x 10(-13), were observed with sampling times of 1 s, 100 s and 1000 s, resp ectively. The overall best value was 9.1 x 10(-14) for a sampling time of 1 0 000 s.