LAUSR

Four lasers from three national metrological institutes (NMIs) were compared in the year 2021 as part of the CCL-K11 ongoing key comparison, initiated by the 13th meeting of the Comité Consultative des Longuers (CCL) in 2007. The absolute frequency of R(127) 11-5 (≈633 nm) and of R(56) 32-0 (≈532 nm) transitions of molecular iodine was measured for these lasers following the technical protocol for CCL-K11. The results of these measurements are compiled in the present report. The comparison reports, as communicated by each participant, are included in the main document. For the very first time in this key-comparison a standard working on a different operating principle is reported. CMI participated with a frequency doubled Nd:YAG laser stabilized to an iodine transition (Designation: CMI-YAG1). The technical protocol was deliberately designed to accommodate artefacts of different wavelengths in a common framework. Moreover, CMI participated with a second laser standard also. The institute has different CMC entries for the two laser types. Both entries refer to the same service category of highest metrological level, but are technically well separated. Due to the layout of CCL-K11 the KCRV is immune to a multiple participation of a single NMI. It was thus considered to include both measurements in this report. This document constitutes the 11th final report for the ongoing key comparison CCL-K11. 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 https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).