J A Stone et al 2009 Metrologia 46 11 doi:10.1088/0026-1394/46/1/002
J A Stone, J E Decker, P Gill, P Juncar, A Lewis, G D Rovera and M Viliesid
Show affiliationsThe Consultative Committee for Length (CCL) has recommended that red (633 nm) unstabilized helium–neon lasers, operating on the 3s2 → 2p4 transition, should be included in the list of standard frequencies for realization of the metre. This paper discusses several topics relating to the recommendation: motivations for including an unstabilized laser in the list of standard frequencies, considerations in assigning a value and an uncertainty for the frequency and vacuum wavelength of the 633 nm transition, and problems associated with the possible presence of 640 nm radiation in the laser output. The fractional uncertainty assigned to the vacuum wavelength of the 633 nm transition is 1.5 × 10−6 (relative standard uncertainty). This uncertainty is sufficiently large to capture all sources of variability associated with construction or operating details of the laser and variations in isotopic mix that might be encountered in commercial laser tubes.
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.55.Lt Gas lasers including excimer and metal-vapor lasers
06.20.Dk Measurement and error theory
Issue 1 (February 2009)
Received 8 April 2008, in final form 16 September 2008
Published 12 December 2008
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