Measuring the In-Process Figure, Final Prescription, and System Alignment of Large Optics and Segmented Mirrors Using Lidar Metrology

The fabrication of large optics is traditionally a slow process, and fabrication capability is often limited by measurement capability. While techniques exist to measure mirror figure with nanometer precision, measurements of largemirror prescription are typically limited to submillimeter accuracy. Using a lidar instrument enables one to measure the optical surface rough figure and prescription in virtually all phases of fabrication without moving the mirror from its polishing setup. This technology improves the uncertainty of mirror prescription measurement to the micronregime. Furthermore, during instrument assembly, a lidar instrument measures the fabricated optical surface directly and compares with scans of diffuse, mechanical surfaces or other coordinate system references on metering structures. This speeds the alignment process and removes the necessity of ancillary alignment fiducials because the optical surface can be sampled directly.