International comparisons of He-Ne lasers stabilized with¹²⁷I₂at     633 nm (July 2000). Part X: Comparison of INMETRO (Brazil), INTI (Argentina), NRC-INMS (Canada), CENAM (Mexico), and BIPM lasers at     633 nm

Abstract

This paper reports the tenth 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 Consultative Committee for Length (CCL), formerly the Consultative Committee for the Definition of the Metre (CCDM), for the periods July 1993 to September 1995 and March 1997 to March 2001. As with the previous nine comparisons, this one 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 seven lasers from four countries in the Americas and the BIPM, meet the goals set by the CCDM in 1992 and in 1997 and adopted by the International Committee for Weights and Measures (CIPM) the same year. The standard uncertainty (1 ) of the frequency of the He-Ne laser stabilized on the saturated absorption of 127 I 2 at λ 633 nm is reduced to a level of 12 kHz (2.5 parts in 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 set to the parameter values normally used in each laboratory; the results then ranged from -31.5 kHz to +10.0 kHz. After checking and correcting when possible the values of all the parameters, the range stayed about the same, -31.5 kHz to +9.1 kHz. Under the latter conditions, the average frequency difference of the group of seven lasers, with respect to the BIPM4 laser, was -4.4 kHz with a standard uncertainty (1 ) of 13.2 kHz. If the INMETRO2 laser, considered as a secondary laser, is removed from the group, then the average is -0.5 kHz with a standard deviation (1 ) of 9.2 kHz. The best relative frequency stabilities, with Allan standard deviations of about 9.3 10 -13 , 3.5 10 -13 and 1.4 10 -13 , were observed with sampling times of 10 s, 100 s and 1000 s, respectively. Results obtained with NRC and BIPM lasers over a period of five months in two beat-frequency laser comparisons and in an absolute frequency measurement lie within 1 kHz (2 parts in 10 12 ).

Long-term absolute frequency measurements of 633 nm iodine-stabilized laser standards at NRC and demonstration of high reproducibility of such devices in international frequency measurements

“…In the past, ensembles of 633 nm laser standards were compared in order to verify the stability of the ensemble-averaged frequencies. Results from comparison data showed that kilohertz level reproducibilities could be observed for the travelling laser systems when values are compared over a period of time [20][21][22]. In general, the relative frequency offsets of the standards constructed in different laboratories were found to satisfy the 10 kHz standard uncertainty set by the CIPM in the 2001 guidelines for the practical realization of the metre [3].…”

“…This conclusion was originally based upon international laser comparisons of INMS 2 during the period 1993 to 2000. In these measurements, the operating frequency was corrected to the mise-en-pratique operating conditions and referenced to the value of the stationary BIPM 4 laser [20][21][22]. Figure 2 that most of the observed change is due to the INMS 2 laser and that the BIPM 4 laser did not drift appreciably in frequency during the period 1993 to 2000.…”

“…As mentioned in section 2, the INMS 2 laser system has been extensively used in international comparisons of 633 nm iodine-stabilized laser systems [20][21][22]. As part of the continuing programme to examine the accuracy and reproducibility of these laser standards and further our understanding of the performance of the NRC frequency comb, the INMS 2 laser system was employed in an international measurement comparison with the BIPM.…”

“…This was followed five months later with an international comparison in which the transportable laser was again compared to BIPM 4 through a transfer laser [20]. The results showed that the frequency of the transportable laser was reproducible such that the two inferred values of the BIPM 4 frequency agreed to below 1 kHz (2 parts in 10 12 ) [22]. Recently, Lea et al [12] reported an evaluation of absolute frequency comparisons and frequency comb measurements spanning a period 1995 to 2002, which indicated that the relative frequencies of the lasers under study had changed no more than 7 parts in 10 12 .…”

The Optical Frequency Standards for the Realization of the Meter

“…The very first formal comparison termed BIPM.L‐K10 was performed from 1989 till 2000 . The frequency standards compared were iodine‐stabilized He–Ne lasers (see Section 4.3 below) operated by 46 NMIs all over the world.…”