Abstract

A design concept and analyis for a long baseline interferometer imaging system that uses real-time higher order wavefront control, tilt and piston control has been developed to: (1) stabilize the fringe field associated with the visibility phases, (2) measure visibility amplitudes and closure phase, and (3) allow investigation of celestial sources beyond 15th magnitude. Pupil plane phase difference control and closure phase measurement on three telescopes is accomplished simultaneously using differential phase modulation and Fourier de composition. Atmospheric wavefromt sensing is accomplished in all three telescopes using Rayleigh scattered 15 watt laser guide stars focused at 20 km. Tilt sensing and correction is accomplished using the imaged source field. A method for obtaining good pupil plane coverage using only three 1 meter apertures is presented. Analysis is performed on the adaptive optics assemblies to trade-off laser guide star power requirements, optical train efficiency, wavefront sensor measuring accuracy, track sensor accuracy, number of wavefront sensor subapertures, deformable mirror actuators and servo bandwidth requirements. Analysis is performed on the piston control subsystem to optimize the measurement of closure phase and visibility amplitude over a narrow spectral bandwidth, to trade-off source irradiance requirements, piston measuring accuracy, and visibility amplitude accuracy.

© 1992 Optical Society of America