Recent results from the imaging beam combiner simulator COSI at the Max-Planck-Institut fuer Extraterrestrische Physik

We present interferograms and reconstructed images obtained with the MPE imaging beam combiner simulator COSI.The purpose of COSI is to simulate the imaging beam combiner at the coherent focus of the ESO VLTI in multi-speckle mode of under conditions of partial or full correction of the single telescope wave front by adaptive optics. The data discussed here were taken in multi-speckle and single speckle mode. COSI consists of a 1-m telescope and a near- IR continuum light source to simulate the radiation from astronomical objects. Two flat mirrors allow us to use one half of the telescope as a transmitter and the other half as a receiver. In the receiving focus we have installed the MPE speckle camera SHARP, which uses a HgCdTe 2562 NICMOS 3 array. A pupil mask over the aperture allows us to simulate various telescope configurations like the one with a beam compression factor of 100 as it will be used for the ESO VLT interferometer. COSI is used to explore NIR array detector properties and their suitability for interferometric measurements and to generate data to develop and test image reconstruction algorithms. First interferograms of single and multiple objects were taken early 1993. Employing various deconvolution and Fourier-inversion methods, a diffraction limited image of the pin-hole sources can be successfully recovered which experimentally demonstrates the feasibility of interferometric imaging with a large monolithic beam combiner. Thus, we have demonstrated that COSI is an excellent test bed to investigate methods of image recovery and to investigate how the methods are influenced by effects like atmospheric turbulence, expected optical imperfections and detector characteristics. Early this year (1994) we installed hot-air seeing simulators for individual subapertures. This allows us now to take interferograms in multi- speckle mode.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.