Comparison of primary standards of length: He-Ne lasers at lambda=633 nm frequency-stabilized to the hyperfine structure of I-2

An international comparison of He-Ne/I-2 lasers at lambda = 633 nm between the CMI (Czech Republic), the OMH (Hungary) and the BEV (Austria) was perfo rmed at the CMI-LPM, Prague, in July 1997 as DUNAMET project D3. The freque ncies of three national standards of length (lasers) were found to be in th e range +/-7 kHz (1.5 parts in 10(11)) and reproducibility of frequency dif ferences between individual lasers during one week was better than +/-5 kHz (1 part in 10(11)). The relative frequency stability, expressed as an Alla n standard deviation, reached a minimum of 3 parts in 10(13) for an integra tion time of 10000 s.