On prospects for an extremely large optical/infrared array telescope

The goal of this study is to investigate the heterodyne interferometer as the basis of an optical receiving array capable of synthesizing source images to extremely high angular resolution, either from a terrestrial site or from space. It is hoped that an angular resolution of one milliarcsecond can be achieved in the presence of the terrestrial atmosphere and that images can be produced of quality comparable with those now obtained with modern synthesis radio telescopes, that is, dynamic range approximately 40 db and field of view of one arcsecond. Such a system, if its sensitivity were sufficient, would find manifold applications in astronomy, in space surveillance, and in remote sensing of the earth and planets from space platforms. Despite the negative evaluations of heterodyne interferometry as a useful astronomical technique at optical wavelengths, based on the perception that insufficient bandwidths would be obtainable, it appears useful to reexamine the potential of this method in the light of recent technological developments. Optical heterodyne methods have been developed to a very workable state of perfection for application to remote sensing problems in atmospheric research and for apolications in fiber optical communications. An attractive feature of the heterodyne technique is that, once the optical or infrared signals have been converted to “intermediate” frequencies, all the successful data-handling methods of radio interferometry can be applied. It is believed that the bandwidth limitation can be overcome by modern methods of electronic integration and data processing, and that the heterodyne method may well provide solutions to the problems of atmospheric inhomogeneity and mechanical precision that have long plagued high-resolution optical astronomy.