Interferometric metrology for a 6.5-meter F/1.25 paraboloidal mirror

Abstract

Optical tests have been designed and analyzed for the interferometric testing of the highly aspheric 6.5-meter F/1.25 primary mirror which was recently cast at the University of Arizona to upgrade the Multiple Mirror Telescope (MMT.) An infrared interferometer using a CO2 laser, a null corrector, and a pyroelectric vidicon will test the surface during loose-abrasive grinding. Precision metrology for the testing of the polished surface will use a visible Shack-cube interferometer co-aligned with a BK7 null corrector, a HeNe laser source, imaging optics, and a CCD array. Both the infrared and visible systems have been carefully designed to give excellent performance in terms of wavefront correction, alignment sensitivity, imaging of the mirror to the detector, diffraction effects, ghost reflections, and ease of use.