Other stabilized lasers
These lasers are used in various length measuring instruments (interferometer) and serve as base for the unit of length. Their wave length is less reproducible as that of the lasers of the former group, therefore they need regular calibration. So called HeNe-Lasers (633 nm) are directly compared by the Iodine-stabilized Lasers BEV1 or BEV2. Lasers working with other wavelengths are calibrated by the femtosecond comb generator.
For the use of these length measuring instruments the deviations of the environmental sensors (air temperature, air pressure, humidity of air) and of the sensors for the material temperature are determined together with the frequency (wavelength) of the integrated laser. Furthermore, the algorithm of the compensation of the wavelength is tested. A system tested in such a way is a very accurate and traceable length measuring instrument.
Electronic distance measuring instruments (EDM), Laser tracker
These length measuring instruments also use a laser radiation source, but their exact wavelength is not so important. They are calibrated at the tape measure comparator.