5. Calibrating a laser interferometer

5.1 Wavelength calibration in vacuum

The frequency (or wavelength in vacuum) of a laser is measured by comparing it with that of a reference laser, using the beat or heterodyning method.

The reference laser is a helium-neon laser slaved to an iodine peak. Its short-term stability is 10 ^–12 . Its reproducibility is of the order of 10 ^–10 . A highly complex measurement chain at the Laboratoire Primaire des Temps et Fréquences links it to the atomic clock (stability 10 ^–13 ) [2] (figure