Precision optics for long baseline interferometry

Optical interferometers are being built to operate over longer and longer baselines, in some cases more than a few kilometers. Examples include laser interferometers to detect gravitational waves, and stellar interferometers which use starlight to determine the angular diameter of the source. The optics used in these interferometers must satisfy demanding performance criteria. In this paper we review some of those criteria and present results which demonstrate that such optical surfaces can be successfully fabricated and measured.