Proceedings Article | 28 June 2006
KEYWORDS: Telescopes, Mirrors, Cameras, Sensors, Interferometry, Deformable mirrors, Phase retrieval, Space telescopes, Image retrieval, Nulling interferometry
The Cophasing Sensor (CS), which measures the disturbances between the sub-apertures, is a key component of multiple-aperture telescopes. As multiple-aperture telescopes become more ambitious, requirements for the CS become more demanding: low flux (for stellar interferometers), sub-nanometric accuracy (for interferometric nullers), image with very small contrast (for wide-field telescopes such as spaceborne Earth imagers), larger number of beams (for all applications). Focal-plane sensing is a solution to cope with all these requirements, with a very simple opto-mechanical setup. Two implementations have been investigated at ONERA: phase retrieval, using the sole focal-plane image, and phase diversity, based on the joint analysis of a focal and an extra-focal images. Phase diversity can measure any mode on any source, while phase retrieval is more suited to real-time piston/tip/tilt measurements on an unresolved (or partially resolved) source. To evaluate accurately the performance of CS or other high-resolution devices, ONERA has built a multipurpose bench called BRISE (Banc Reconfigurable d'Interferometrie sur Sources Etendues). BRISE mainly includes an extended scene and a reference point source, a deformable mirror, a focal-plane CS, afocal input/output ports to interface with other instruments, and a general purpose code MASTIC (Multiple-Aperture Software for Telescope Imaging and Cophasing). BRISE has already been (or will be) used for several applications, such as the validation of CSs for Earth imaging or nulling interferometry, or the exploration of advanced nulling techniques. This paper describes the bench and the investigated CSs, the experiments performed on BRISE, and reports main results such as nanometric accuracy or three-beam nulling.
