Wavelength Measurements of the Iodine Stabilized Helium-Neon Laser

This paper compares measurements of the wavelength of an NPL constructed iodine stabilized laser, made in terms of the 86 Kr primary standard which were carried out at the BIPM, with an earlier measurement at NPL. The result of the BIPM measurements for the i component of 127 I 2 is λ ( 127 I 2 , i) = [632991 399.7 ± 0.2] fm and differs by only 0.7 fm (1 × 10 -9 ) from the NPL result made on the same laser. The results provide an illustration of the reproducibility of the 86 Kr standard which is now considered to be of the order of 4 × 10 -9 , and also illustrate the ability of the two laboratories with their different measurement techniques to perform high precision wavelength measurement. Some preliminary beat frequency measurements of the frequency reproducibility of BIPM and NPL lasers are also reported.