Radiations of the "mise en pratique"
The laboratory realises the definition of the unit of length, the metre, and maintains and disseminates the standards for the wavelength. It provides the Italian primary standards and therefore ensures the traceability to the length unit over the country.
The laboratory fulfils the CIPM Mutual Recognition Arrangement and therefore regularly participates to the international key comparisons and it is kept under a rigorous quality system.
The metre is realised by two alternative methods: a) by the measurement of the absolute frequency of a laser source b) by means of the “mise en pratique”. In the former case, the frequency of a laser is measured by a frequency comb to determine the vacuum wavelength of the radiation λ0 from the relation λ0 = c / f, where c is the speed of light in vacuum. In the latter case, the frequency of the laser is actively stabilised over one of the radiations recommended by the Comité Consultif pour la Longeur.