METAS Gauge Block Interferometer

The METAS gauge block interferometer for long gauge blocks consists of a vibration-damped optical measurement table equipped with a laser interferometer setup and a temperature- and sound-insulated enclosure with a hinged cover. The measurement table supports the interferometer optics, while the camera used for image processing is mounted on the enclosure. All additional electronic measuring instruments are housed in an electronics rack with direct ventilation.

To determine an unambiguous gauge block length, the number of complete interference fringes N must be determined. This is achieved through a mechanical preliminary determination of the length combined with phase measurements at three different wavelengths. Three lasers are used: a red mode-stabilised He-Ne laser, a green mode-stabilised He-Ne laser and a green iodine-stabilised Nd laser.

The calibration value of the gauge block length is determined using the green iodine-stabilised Nd laser . The red He-Ne laser , which is calibrated by direct comparison with the primary realisation of the metre, is used for validation. The green mode-stabilised He-Ne laser is used to verify N.