This paper reports the fifth 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 period July 1993 to September 1995. The results of this comparison, involving six lasers from five countries and the BIPM, meet the goals set by the CCDM in 1992 and adopted by the Comité International des Poids et Mesures (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 or the CSIRO1 lasers, with all the lasers set to the parameter values normally used in each laboratory; the results ranged from -48.3 kHz to 13.8 kHz. After checking and readjusting the values of all the parameters, the range was reduced to -14.7 kHz to 10.4 kHz. Under the latter conditions, the average frequency difference of the group of lasers with respect to the BIPM4 laser was -0.5 kHz with a standard uncertainty (1 ) of 8.5 kHz. The best relative frequency stabilities, with Allan standard deviations of about 3.5 parts in 10 12 and 3.5 parts in 10 13 , were observed with sampling times of 8 s and 2048 s, respectively.
A comparison of iodine cells used to stabilize helium-neon lasers was carried out by three standards laboratories, the Bureau International des Poids et Mesures (BIPM), the National Measurement Laboratory (NML/CSIRO), Australia, and the Measurement Standards Laboratory (MSL) of the New Zealand Institute for Industrial Research and Development. The frequencies produced by any of the cells in any of the lasers at each laboratory agreed to within 1 part in 1011 (4,7 kHz).
The results of the APMP key comparison on calibration of gauge blocks by interferometry (APMP.L-K1) are reported. The comparison involved the measurement, by ten participating institutes, of eight steel gauge blocks and ten ceramic gauge blocks ranging from 0.5 mm to 100 mm in length using techniques based on interferometry. The results are analysed using En values with weighted mean values as the reference values. Some measurement results had to be excluded by application of the En-criterion for the steel and ceramic gauges. Investigations of the reasons for the deviations have already been started by the respective institutes, including follow-up gauge block comparison, APMP.L-K1.1 with the same pilot laboratory as APMP.L-K1.Main text. To reach the main text of this paper, click on Final Report.
Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
This paper describes improvements to a Hilger gauge block interferometer, including a fibre optic feed for a traceable laser radiation, use of a CCD camera for computer-controlled acquisition of fringe images and automatic analysis of the fringe image to obtain the fringe fraction. The gauge measuring process is now automated, computer-controlled, more accurate and significantly faster and easier to operate than the original design.
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