Measurements of large optical surfaces with a laser tracker

Surface measurements represent a significant part of the cost for manufacturing large aspheric optics. Both polished and rough ground surfaces must be measured with high precision and spatial resolution. We have developed a system that couples a commercial laser tracker with an advanced calibration technique and a system of external references. This system was built to measure the off-axis primary mirror segments for the Giant Magellan Telescope where it will guide loose abrasive grinding and initial polishing. The system is further expected to corroborate the optical interferometric tests of the completed mirrors, in several low-order aberrations. The design, analysis, calibration, and measured performance of this system will be presented.