SCOTS: a reverse Hartmann test with high dynamic range for Giant Magellan Telescope primary mirror segments

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.

[1]  K. Law,et al.  Production of 8.4m segments for the Giant Magellan Telescope , 2012, Other Conferences.

[2]  Tom L. Zobrist,et al.  Accuracy of laser tracker measurements of the GMT 8.4 m off-axis mirror segments , 2010, Astronomical Telescopes + Instrumentation.

[3]  Chunyu Zhao,et al.  Orthonormal vector polynomials in a unit circle, Part I: Basis set derived from gradients of Zernike polynomials. , 2007, Optics express.

[4]  Werner P. O. Juptner,et al.  High-resolution 3D shape measurement on specular surfaces by fringe reflection , 2004, SPIE Photonics Europe.

[5]  D. Malacara-Doblado,et al.  Hartmann, Hartmann–Shack, and Other Screen Tests , 2006 .

[6]  James H. Burge,et al.  Scanning pentaprism test for the GMT 8.4-m off-axis segments , 2010, Astronomical Telescopes + Instrumentation.

[7]  Tom L. Zobrist,et al.  Use of a commercial laser tracker for optical alignment , 2007, SPIE Optical Engineering + Applications.

[8]  Markus C. Knauer,et al.  Phase measuring deflectometry: a new approach to measure specular free-form surfaces , 2004, SPIE Photonics Europe.

[9]  James H. Burge,et al.  Development of surface metrology for the Giant Magellan Telescope primary mirror , 2008, Astronomical Telescopes + Instrumentation.

[10]  Chunyu Zhao,et al.  Orthonormal vector polynomials in a unit circle, Part II : Completing the basis set. , 2008, Optics express.

[11]  J. L. Rayces.  Exact Relation between Wave Aberration and Ray Aberration , 1964 .

[12]  Tom L. Zobrist,et al.  Alignment and use of the optical test for the 8.4-m off-axis primary mirrors of the Giant Magellan Telescope , 2010, Astronomical Telescopes + Instrumentation.

[13]  Matt Johns.  The Giant Magellan Telescope (GMT) , 2006, SPIE Astronomical Telescopes + Instrumentation.

[14]  Mourad Idir,et al.  Non-null full field X-ray mirror metrology using SCOTS: a reflection deflectometry approach. , 2012, Optics express.

[15]  Lirong Wang,et al.  Software configurable optical test system: a computerized reverse Hartmann test. , 2010, Applied optics.