VLTI delay line — 1

The VLTI Delay Line retroreflector carriage moving along its rails in the Interferometric Tunnel. The Delay Line is a mechanical-optical system that compensates the optical path differences of the light beams from the individual telescopes. Such a system is necessary to ensure that the light from all telescopes arrives in the same phase at the focal point of the interferometer. Otherwise, the light cannot be successfully combined interferometrically.