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Advances in optical testing are as important as advances in fabrication because one can make only what one can measure. A high-precision metrology capability is utilized to close the gap between interferometric testing and lower precision metrology, laser radar, or contact-probe-based coordinate measuring machines (CMM) to accurately measure surfaces with large form error. This nearly universal optical testing method employs a precision CMM equipped with a non-contact, confocal probe. This technique was developed to characterize and align a broad spectrum of optical surfaces including ones with high slopes that are nearly impossible to measure using traditional interferometric testing without custom-made optics. Optical components covering a wide range of prescriptions, such as large convex conics, high-sloped aspherics, grazing-incidence x-ray optics, and highly deformed flats, were successfully measured. The resulting data were processed using custom-developed routines to determine the optic’s alignment, the departure from design surface, and the as-built prescription parameters. This information was used to verify and guide the development and fabrication of novel optics.

Optical designs for the next generation space science instruments call for unconventional, aspheric, and freeform (FF), prescriptions with tight tolerances. These advanced surfaces enable superior-performance, compact, and lower cost systems but are more challenging to characterize and, hence, to fabricate and integrate. A method was developed to characterize a wide range of optical surfaces, without requiring custom-made correctors, and to align them to each other for a high-performance optical system. A precision coordinate measuring machine, equipped with a non-contact, chromatic confocal probe, was used to measure numerous optics including large convex conics, high-sloped aspherics, several FF surfaces, and grazing-incidence x-ray optics. The resulting data were successfully reduced using custom-developed, advanced surface fitting analysis tool, to determine the optic’s alignment relative to the global and local coordinate systems, surface departure from design, and the as-built optical prescription. This information guided the modeling and the alignment of the corresponding as-built optical systems, including a flight system composed of a three-mirror anastigmat.

CMM metrology provides simple, 3D surface data used for prescription retrieval, figure error, and alignment with high accuracy without null-correctors. Two freeform mirrors for a compact telescope were successfully characterized and aligned using the CMM.

The only way to increase the sensitivity of X-ray telescopes without significantly increasing their size (compared to existing telescopes) is to use thinner mirror shells. However, to maintain the figure of thin mirror shells, their shape will need to be adjusted after they are mounted and/or actively controlled during flight. Here we describe progress toward developing a method that can be used to do both. The core of the concept is to coat thin (

NASAs James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element which contains four science instruments (SIs). Prior to integration with the spacecraft, the JWST optical assembly is put through rigorous launch condition environmental testing. This work reports on the metrology operations conducted to determine any changes in subassembly alignment, including primary mirror segments with respect to each other, the secondary mirror to its support structure, the tertiary mirror assembly to the backplane of the telescope and ultimately to the ISIM.

The final, flight build of the Integrated Science Instrument Module (ISIM) element of the James Webb Space Telescope is the culmination of years of work across many disciplines and partners. This paper covers the large volume, ambient, optical and opto-mechanical metrology techniques used to verify the mechanical integration of the flight instruments in ISIM, including optical pupil alignment. We present an overview of ISIM's integration and test program, which is in progress, with an emphasis on alignment and optical performance verification. This work is performed at NASA Goddard Space Flight Center, in close collaboration with the European Space Agency, the Canadian Space Agency, and the Mid-Infrared Instrument European Consortium.

Absolute measurement with SCOTS/deflectometry is a calibration problem. We use a laser tracker to calibrate the test geometry. The performance id demonstrated with the initial measurement results from the Large Synoptic Survey Telescope tertiary mirror. Systematic errors from the camera are carefully controlled. Camera pupil imaging aberration is removed with an external aperture stop. Imaging aberration and other inherent errors are suppressed with a rotation test. Results show that the SCOTS can act as a large dynamic range, high precision, non-null test method for precision aspheric optics. The SCOTS test can achieve measurement accuracy comparable with the traditional interferometric testing.

A software configurable optical test system (SCOTS) based on fringe reflection was implemented for measuring the primary mirror segments of the Giant Magellan Telescope (GMT). The system uses modulated fringe patterns on an LCD monitor as the source, and captures data with a CCD camera and calibrated imaging optics. The large dynamic range of SCOTS provides good measurement of regions with large slopes that cannot be captured reliably with interferometry. So the principal value of the SCOTS test for GMT is to provide accurate measurements that extend clear to the edge of the glass, even while the figure is in a rough state of figure, where the slopes are still high. Accurate calibration of the geometry and the mapping also enable the SCOTS test to achieve accuracy that is comparable measurement accuracy to the interferometric null test for the small- and middle- spatial scale errors in the GMT mirror.

A software configurable optical test system (SCOTS) based on deflectometry was developed at the University of Arizona for rapidly, robustly, and accurately measuring precision aspheric and freeform surfaces. SCOTS uses a camera with an external stop to realize a Hartmann test in reverse. With the external camera stop as the reference, a coordinate measuring machine can be used to calibrate the SCOTS test geometry to a high accuracy. Systematic errors from the camera are carefully investigated and controlled. Camera pupil imaging aberration is removed with the external aperture stop. Imaging aberration and other inherent errors are suppressed with an N -rotation test. The performance of the SCOTS test is demonstrated with the measurement results from a 5-m-diameter Large Synoptic Survey Telescope tertiary mirror and an 8.4-m diameter Giant Magellan Telescope primary mirror. The results show that SCOTS can be used as a large-dynamic-range, high-precision, and non-null test method for precision aspheric and freeform surfaces. The SCOTS test can achieve measurement accuracy comparable to traditional interferometric tests.