Active distance stabilization of large bodies using Fabry-Perot interferometry

Presents control design and results of a distance stabilization experiment aiming at picometre repeatability. The experiment, called COSI, was funded by the European Space Agency in view of space telescopes needing picoradian precision. Stabilization is achieved by actively controlling the optical length of in-vacuum Fabry-Pe´rot interferometers. Experiments stabilized three 0.5-m distances between two 7-kg plates with a repeatability better than 3 pm (1σ), in presence of severe environmental noise and artificial micrometre displacements, thus demonstrating the feasibility of the COSI concept and technology