Recommendation 2 of the 96th CIPM (2007)

On the value and uncertainty of unstabilised He-Ne lasers

The International Committee for Weights and Measures,

considering

• that most laser interferometers and many other measuring instruments used for length measurement are based on 633 nm He-Ne lasers;
• that these instruments are often used at uncertainty levels that are large compared to the possible variation of the He-Ne laser vacuum wavelength;
• that the vacuum wavelength of the unstabilized 633 nm He-Ne laser is restricted to within a narrow range by fundamental quantum phenomena;

recognizing

• that it would be necessary to provide guidance and documentary evidence concerning the value of the vacuum wavelength and its uncertainty that can be expected in the absence of calibration;
• that such evidence could help to avoid unnecessary calibrations of these lasers in such applications;

recommends

• that the values
  f = 473.612 7 THz
  λ = 632.990 8 nm
  with a relative standard uncertainty of 1.5 × 10^–6, apply to the radiation in vacuum of a unstabilised helium-neon laser operating solely on the 3s₂→2p₄ transition, independent of the isotopic mixture of the neon;
• that an entry for unstabilized helium-neon lasers, operating on the 633 nm (3s₂→2p₄) neon transition, be included in the second category of the list of standard frequencies, and that an accompanying paper with CCL authority be published in Metrologia.

DOI : 10.59161/CIPM2007REC2E