Fabrication and testing of the first 8.4-m off-axis segment for the Giant Magellan Telescope

Martin, Hubert M.; Allen, R. G.; Burge, James H.; Kim, D. W.; Kingsley, J. S.; Tuell, Michael T.; West, Steve C.; Zhao, Chunyu; Zobrist, T.

doi:10.1117/12.857494

Cited by 30 publications

(16 citation statements)

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“…At the present time the alignment procedures are working to within about a factor of two of the required final precision, and work is proceeding to reduce the measurement errors to the required final values. The production and testing of the first GMT mirror are described in greater detail by Martin et al 3 An account of the alignment procedure for the principal optical test is given by West et al 4 The principal test can only be used once the mirror has been polished to produce a specular reflection with residual slope errors of moderate amplitude. During generating and fine grinding the surface is measured using a laser tracker supplemented by four additional laser interferometers which monitor dimensional changes in the test tower while the test is in progress.…”

Section: Opticsmentioning

confidence: 99%

GMT overview

Shectman¹,

Johns²

2010

SPIE Proceedings

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The 25-meter Giant Magellan Telescope (GMT) is one of the next generation of extremely large ground-based optical/infrared telescopes. GMT is currently under development by a consortium of major US and international university and research institutions. The telescope will be located at the Las Campanas Observatory in Chile. The GMT Project is mid-way through its Design Development Phase. This paper summarizes the organizational structure and status of the GMT Project and recent progress in the technical development of the various GMT subsystems.

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Section: Opticsmentioning

confidence: 99%

GMT overview

Shectman¹,

Johns²

2010

SPIE Proceedings

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“…Reload initial driver coefficients and clear all gauge data to zeros. 4. Reload driver coefficients of step 2; save gauge data after lap surface becomes stable.…”

Section: Measurement Of Active Stressed Lap Surfacementioning

confidence: 99%

“…During processing, the lap could follow the shape of an aspheric surface under the control of 12 or more actuators, which makes the fabrication of large aspheric surfaces as easy as that of spheric surfaces. In the past decade, mirrors with 1.2-8.4 m diameter have been fabricated with high performance by using active stressed lap technology [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Deformation verification and surface improvement of active stressed lap for 4 m-class primary mirror fabrication

Zhao

Fan

et al. 2015

Appl. Opt.

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The surface shape accuracy of the active stressed lap impacts the performance of grinding and polishing in the fabrication of large mirrors. We introduce a model of active stressed lap for the fabrication of a 4 m f/1.5 mirror based on finite element analysis (FEA), and the lap surface accuracy achieves RMS<1.8 μm in the FEA method. Using the lap surface measurement system, experimental verification is put forward, and the RMS of the measured lap surface is within 2 μm in practice. A general improvement in lap surface accuracy using the Zernike polynomial is shown. After compensating the calculation errors, the lap surface accuracy is improved by 8%-23%, and achieves RMS<1.5 μm, which is appropriate for practical grinding and polishing.

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“…[1]- [3] The Laser Tracker Plus system uses a high precision laser tracker to measure the position of a tracker ball that is scanned across the surface of the mirror. The principal optical test uses a hologram and two spherical mirrors to produce a wavefront that can be used to do an interferometric null test on the mirror.…”

Section: Introductionmentioning

confidence: 99%

Scanning pentaprism test for the GMT 8.4-m off-axis segments

Allen

Burge

et al. 2010

SPIE Proceedings

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The scanning pentaprism system for testing the 8.4 m off-axis segments for the Giant Magellan Telescope has recently been completed. The system uses a fiber source and a carriage mounted pentaprism to scan a 40 mm collimated beam across the surface of the segment under test. Since the scanning beam is parallel to the optical axis of the parent mirror, it comes to focus on a detector at the telescope's prime focus, where displacement of the spot is proportional to the slope error. A second collimated beam from a stationary reference pentaprism is used to compensate for any changes in the relative positions of the optical components during testing. The optical components are suspended over the mirror on a rail system that can be rotated so that scans can be made across any diameter of the segment. The test is capable of measuring wavefront slope errors to 1 μrad rms, adequate to verify that power, astigmatism, coma, and other low-order aberrations are small enough to be corrected easily at the telescope with the segment's active support system.

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Fabrication and testing of the first 8.4-m off-axis segment for the Giant Magellan Telescope

Cited by 30 publications

References 0 publications

GMT overview

GMT overview

Deformation verification and surface improvement of active stressed lap for 4 m-class primary mirror fabrication

Scanning pentaprism test for the GMT 8.4-m off-axis segments

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