Is laser vacuum wavelength an intrinsic standard, automatically traceable to the SI unit of length?
There is no clear-cut, widely accepted answer to this question, largely because of various problems discussed below (see caveats at the end of this FAQ). However, arguments in favor of this viewpoint can be made for the case of the red helium neon (He-Ne) laser most widely used in industry. As discussed below, the vacuum wavelength of a He-Ne laser operating on the standard red transition (3s2→2p4) cannot deviate by more than two or three parts in 106 from its nominal value. The vacuum wavelength is set by the atomic structure of the neon atom and in that sense it is an intrinsic standard. If you do not need accuracy better than a few parts in 106, it is our opinion that there would be nothing gained by actually measuring the vacuum wavelength. If you need greater accuracy, the vacuum wavelength may be determined by comparison with an iodine-stabilized laser. If you would like us to measure the vacuum wavelength of your lasers, you can make arrangements with Jack A. Stone. If the backg
For arbitrary lasers, there is no clear-cut and widely accepted answer to this question. However, persuasive arguments in favor of this viewpoint have been made for the case of the red helium neon (He-Ne) laser most widely used in industry, subject to several caveats discussed at the end of this FAQ. The Consultative Committee for Length of the BIPM (International Bureau of Weights and Measures) subscribes to this viewpoint. (see J. A. Stone et.al., Metrologia 46 (2009) 11-18). As discussed below, the vacuum wavelength of a He-Ne laser operating on the standard red transition (3s2→2p4) cannot deviate by more than two or three parts in 106 from its nominal value. The vacuum wavelength is set by the atomic structure of the neon atom and in that sense it is an intrinsic standard. If you do not need accuracy better than a few parts in 106, it is our opinion that there would be nothing gained by actually measuring the vacuum wavelength. If you need greater accuracy, the vacuum wavelength ma
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