Abstract
The Optical Metrology Division (Diopt) of Inmetro is responsible for maintaining the national reference of the length unit according to International System of Units (SI) definitions. The length unit is realized by interferometric techniques and is disseminated to the dimensional community through calibrations of gauge blocks. Calibration of large gauge blocks from 100 mm to 1000 mm has been performed by Diopt with a Koesters interferometer with reference to spectral lines of a krypton discharge lamp. Replacement of this lamp by frequency stabilized lasers, traceable now to the time and frequency scale, is described and the first results are reported.
Highlights
In the early 1970s the team of John Hall of the NBS realized the first frequency chain connecting the microwave frequency of the cesium atomic clock to the frequency of a methane-stabilized helium-neon laser at 88.4 THz [1]
In the early 1980s it was possible to measure the frequency of some iodine stabilized He-Ne lasers allowing in 1983, during the 17th General Conference on Weights and Measures, a new definition of the meter, defined as “the path length traveled by light in vacuum during a time interval of 1/299 792 458 second” [2,3]
Among these there are a radiation of He-Ne laser, stabilized to the a16 component of the 2I127 R(127) 11-5 hyperfine transition, which currently corresponds to the national primary length standard, and radiation transitions corresponding to 5d5-2p10, 2p8-5d4 and 1s3-3p10 of the krypton spectral lamp (86Kr), used as the working length standard in the interferometer Koesters
Summary
In the early 1970s the team of John Hall of the NBS (renamed afterward as NIST) realized the first frequency chain connecting the microwave frequency of the cesium atomic clock to the frequency of a methane-stabilized helium-neon laser at 88.4 THz [1]. In the early 1980s it was possible to measure the frequency of some iodine stabilized He-Ne lasers allowing in 1983, during the 17th General Conference on Weights and Measures, a new definition of the meter, defined as “the path length traveled by light in vacuum during a time interval of 1/299 792 458 second” [2,3] This definition fixes the speed of light to an exact value, requiring for the determination of the vacuum wavelength of a radiation through the measurement of its frequency [4]. 8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015 1 different frequencies, phasing out the becoming obsolete spectral lamps With this substitution it is possible to further improve measurement capability, since the laser light provides sharper and more intense interference fringes for easier viewing or image capture with digital cameras to carry out the reading of the fringe pattern. This enables process automation, reducing measurement uncertainties and false operator judgments
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