BEAM COMBINER CONCEPT FOR THE DARWIN IMAGING MODE

摘要

Darwin will spend part of the mission lifetime carrying out aperture synthesis imaging of star- and planet-forming regions, quasars and very distant galaxies in the 6-18 micron wavelength range. A wide field of view of at least 1" is highly desirable to fully exploit the scientific potential of the mission. This could be achieved by configuring Darwin as a Fizeau interferometer, where the recombining beams are arranged so to form a scaled replica of the instantaneous array configuration (homothetic mapping). However, pupil mapping is not easily implemented in space. Particularly troublesome in this regard are the need for cryogenic positioning devices with strokes of several hundreds of millimeters, and the large mass and volume of such a beam combiner. We propose a novel way to perform homothetic mapping on space interferometers, where the configuration of the recombining beams is fixed, while their diameter is changed during array reconfiguration. Using Darwin as a test case, we show that this variable-magnification approach can be realized with substantially simpler hardware as compared to conventional mapping. In particular, actuator stroke requirements are relaxed to a few tens of mm. We also emphasize the potential of this method to lead to compact Fizeau beam combiner implementations, which is of great relevance for Darwin and other future space missions.