Abstract. This paper reports the eighth set of results of a series of grouped laser comparisons from national laboratories undertaken by the Bureau International des Poids et Mesures (BIPM) at the request of the Comité Consultatif pour la Définition du Mètre (CCDM, now the Consultative Committee for Length, CCL) during the periods July 1993 to September 1995 and March 1997 to July 1997. This comparison, like the previous seven, is expected to be listed as a key comparison in the context of the ongoing BIPM.L-K10 series.

The results of this comparison involving five lasers, four from three countries of the Asia-Pacific group and one from the BIPM, meet the goals set by the CCDM in 1992 and adopted by the International Committee of Weights and Measures (CIPM) the same year. The standard uncertainty (1 σ) of the frequency of the He-Ne laser stabilized on the saturated absorption of ¹²⁷I₂ at 633 nm is reduced to the level of 12 kHz (2.5 × 10¹¹) when the lasers compared meet the recommended values of the parameters.

The lasers were first compared with the BIPMP3 laser, with all the lasers set to the parameter values normally used in each laboratory; the results then ranged from −112.7 kHz to +24.9 kHz. After checking and correcting the values of all the parameters and replacing a contaminated iodine cell, the range was reduced to −31.5 kHz to +14.3 kHz. Under the latter conditions, the average frequency difference of the group of lasers, with respect to the BIPM4 laser, was −1.9 kHz with a standard uncertainty (1 σ) of 20.2 kHz. The best frequency stabilities, with relative Allan standard deviations of about 6.6 × 10¹², 6.0 × 10¹³ and 1.3 × 10¹³, were observed with sampling times of 1 s, 100 s and 1000 s, respectively. The overall best value was 9.5 × 10¹⁴ for a sampling time of 6000 s.

Print publication: Issue 2 (April 2001)