Abstract

Since 1983 we have operated the 6.86-m multiple mirror telescope (MMT) as a cophased optical array for diffraction-limited interferometric imaging in visible wavelengths. We have obtained seeing calibrated diffraction-limited images of the point source Gamma Orionis in various bandpasses to validate the imaging performance of the system as a function of wavelength (410–850 nm) and of coherence length (6 μm to 3.6 mm). We find a stable point spread function with full width at half-power of 75 nrad (0″015 sec of arc) at 500-nm wavelength, as would be expected for the unaberrated aperture imaging an unperturbed wavefront. We have obtained images of the red supergiant Alpha Orionis both in the chromospheric Hydrogen-Alpha emission and in an adjacent continuum wavelength with λ²/Δλ = 3.6 mm, and of a geosynchronous communications satellite in a broader bandpass at 550 nm with λ²/Δλ = 30 μm. In both extremes the resolution in the images is consistent with the observed point spread functions. Although the MMT optics support structure flexes, allowing up to 500 μm of differential variations in optical path lengths as a function of elevation, these elevation-dependent variations are modeled by quadratic functions and removed by our open-loop cophasing system.

© 1986 Optical Society of America