Experimental verification of field extension for non-homothetic arrays with a pupil-plane interferometer

Wide field interferometry has become a subject of increasing interest in the recent years. New methods have been suggested in order to avoid the drawbacks of the standard wide field method (homothetic mapping) which is not applicable when the aperture is highly diluted; for this reason imaging with non-homothetic arrays is being extensively studied1,2. The field of view of a pupil plane interferometer or a densified array consists only of a few resolution elements; in order to improve these systems, we developed a new method consisting of a Michelson pupil-plane combination scheme where a wide field of view can be achieved in one shot. This technique, called "staircase mirror" approach, has been described in a previous paper3 and uses a stair-shaped mirror in the intermediate image plane of each telescope in the array, allowing for simultaneous correction of the differential delay for the on and off-axis image positions. Experimental results have been obtained recovering the fringes of off-axis stars with an angular separation of approximately 1 arcmin simultaneously, and with a contrast similar to that of the on-axis reference star. With this example, we demonstrate an increase of the field of view by a factor of five, with no need of extra observation time. An algorithm to recover the visibilities from the stars focused on the edge of the steps is described and experimental results are shown that prove that a continuous wide field of view can be acquired in one shot.