Optical design, modelling and tolerancing of a Fizeau interferometer dedicated to astrometry

¹ DESPA, Observatoire de Paris, F-92195 Meudon Cedex, France
² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, U.S.A.

Received: 19 September 1995
Accepted: 2 November 1995

Abstract

Space-based interferometers dedicated to wide-angle astrometry would dramatically increase the accuracy of angular measurements fundamental to a wide range of astrophysical problems. The proposed Global Astrometric Interferometer for Astrophysics (GAIA), a continuously rotating instrument comprising two or three interferometers, will reach the as level on more than 35 million objects. The necessary wide field-of-view for such a precision could be obtained with a Fizeau interferometer. We designed and modelled a 2.6 m baseline interferometer with two 40 cm apertures, and overall dimensions compatible with the size of the Ariane V payload shroud. It has a ~ 1 degree diffraction limited field-of-view. The response of the optical system to small perturbations on each optical element is given in terms of fringe visibility, which is shown to depend mainly on sub-aperture spot separation. The robustness of the design to thermal, mechanical and manufacturing errors is discussed.