FIELD ROTATOR FOR THE GI2T INTERFEROMETER

A field rotator dedicated to compensate for the celestial field rotati on has been designed and built for the Grand Interferometre a 2 Telesc opes (GI2T) by the Laboratoire d'Astronomie Spatiale (LAS). In each in terferometric arm, we introduce a three-reflection optics rotatable ar ound ?he axis of the optical train. Since the visibility of the interf erence fringe pattern is mostly sensitive to the differential instrume ntal polarization, this device must fulfill not only optomechanical re quirements but also polarization constraints. For this purpose, three metallic reflections at small incidences are preferred to classical K- prisms (such as Dove or Koenig-Abbe prisms) and coatings optimization leads to protected silver mirrors. (C) 1998 Society of Photo-Optical i nstrumentation Engineers.