Dimensional measurements using laser interferometry

On October 20, 1983, the 17th General Conference on Weights and Measures at the BIPM decided to adopt a new definition of the metre, as follows:

"The metre is the length of the path travelled by light in a vacuum for a duration of 1/299,792,458 of a second.

With this definition, the value of the speed of light in a vacuum is exactly :

Previous definitions of the metre (the Mètre Étalon in platinum, deposited at the Pavillon de Breteuil, then the definition based on the orange line of the krypton 86 spectral lamp) were successively abandoned in favour of a more precise definition.

Interferometric length or displacement measurements, the subject of this article, involve comparing this length with the wavelength of the radiation used. The wavelengths of light radiation in the visible range are between 0.4 µm (violet) and 0.7 µm (red). This method of measurement is therefore directly related to the definition of the unit of length.

The use of frequency-stabilized lasers instead of spectral lamps has contributed to the development of interferometric measurements, even in industrial environments.