Abstract

A design concept and analysis for a long interferometer imaging system that uses realtime higher wavefront control, tilt and piston control has been developed to: (1) stabilize the fringe field associated with the mutual coherence function, (2) measure visibility amplitude and closure phase, and (3) allow the investigation of celestial sources at lease down to 15th magnitude. Pupil plane piston phase control and closure phase measurement is accomplished on three 1-m apertures simultaneously by differential phase modulation and Fourier decomposition. Atmospheric wavefront sensing is accomplished in all three telescopes using Rayleigh scattered 15-W laser guide stars focused at 20 km. Tilt sensing and correction is accomplished using the imaged source field. Analysis is performed on the wavefront control assembly to tradeoff laser guide star power requirements, optical train efficiency, wavefront sensor measuring accuracy, number of wavefront sensor subapertures, deformable mirror actuators and servo bandwidth requirements. Analysis is performed on the tilt stabilization system to tradeoff source field irradiance requirements, optical train efficiency, track sensor accuracy and servo bandwidth. Analysis is performed on the piston control sub-system to optimize the measurement of closure phase and visibility amplitude over a narrow spectral bandwidth, to tradeoff source field irradiance requirements, piston measuring accuracy, and visibility amplitude accuracy.

© 1991 Optical Society of America