Production of 8.4m segments for the Giant Magellan Telescope

Martin, Hubert M.; Allen, Richard G.; Burge, James H.; Kim, D. W.; Kingsley, J. S.; Law, K.; Lutz, R. D.; Strittmatter, P. A.; Su, Peng; Tuell, Michael T.; West, S. C.; Zhou, Ping

doi:10.1117/12.926347

Cited by 27 publications

(7 citation statements)

References 12 publications

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“…[2][3][4][5][6][7][8][9][10] . From the classical Preston equation, we know that the material removal rate R of zerodur can be expressed as follows [2][3][4][5][6][7][8][9][10] , Different polishing method has different polishing conditions. First the mirror is polished by rapid polishing, and then it is polished by precision polishing based on our existing experiment conditions.…”

Section: Methodsmentioning

confidence: 99%

Study on optical polishing experiment of zerodur mirror

Wang¹,

Li²,

Wang³

et al. 2014

SPIE Proceedings

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A zerodur mirror whose aperture is 900mm is chosen to be the primary mirror of an optical system. The mirror is polished by rapid polishing and precision polishing methods relatively. The final surface figures of the mirror are as follows: the peak-to-valley value (P-V value) is 0.204λ (λ=632.8nm), and the root-mean-square value (RMS value) is 0.016λ, which meet the requirement of the optical system. The results show that the polishing process is feasible.With the rapid development of modern optical remote sensing, new requirements such as large field of view, high resolution and high signal-to-noise ratio are proposed to the optical system. Therefore, large-apertured aspheric mirror is applied widely as the primary mirror of optical system. The choice of the materials of the mirror is very important to the performance of the optical system. Proper mirror materials should have excellent physical properties as follows, high stiffness, low density, low coefficient of thermal expansion, high coefficient of thermal conductivity, good processability for optical manufacturing, excellent stability, and etc.. Low density means that the mass of both the mirror and its supporting structure are low. High ratio of stiffness to density means that we can get excellent mechanical performance, i.e. the deformation of the mirror caused by load is so low that the mirror has better performance to resist the stress of polishing, assemblage and self-weight. Low coefficient of thermal expansion means that the structure dimension of the mirror changes less. High coefficient of thermal conductivity means that the mirror is easy to maintain the surface figure which is designed.The standard mirror materials are as follow, silicon carbide (SiC), beryllium (Be), ultra-low-expansion glass (ULE), zerodur, fused silica, K9 glass and etc. [1] . The properties of the materials are listed in Table 1. From the table, it can be seen that Be has the most excellent mechanical performance, it not only has the highest coefficient of thermal expansion, but also is poisonous, which restricts its application. The mechanical performance of SiC is excellent, but it has relative high coefficient of thermal expansion, and it is more difficult to manufacture than ULE, Zerodur, fused silica and K9 glass. The stability of fused silica is not good. The coefficient of thermal expansion of K9 glass is high while its Young's modulus is low. ULE and zerodur are the better materials for their excellent thermal stability and processability. Therefore, ULE and zerodur have large field of application for their relative mature processing and optical manufacturing technologyies. Since zerodur has better mechanical properties and is easier to obtain than ULE, the choice of zerodur is reasonable. Table 1 Properties of the standard mirror materials Type of materials Density (Kg/m 3 ) Young's modulus (Gpa) Ratio of stiffness to density(GNmKg -1 ) Poisson's ratio Coefficient of thermal expansion (10 -6 K -1 ) Coefficient of thermal conductivity (Wm -1 K -1 ) SiC 3080 350 0.11 0...

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Section: Methodsmentioning

confidence: 99%

Study on optical polishing experiment of zerodur mirror

Wang¹,

Li²,

Wang³

et al. 2014

SPIE Proceedings

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“…This maintains the tool's rigid behavior to preserve the smoothing efficiency within a local tool stroke timescale. The RC lap's as-built performance was successfully demonstrated by completing the 8.4 m GMT off-axis primary mirror with 13 mm of freeform departure at the RFCML [3].…”

Section: Conformal Fabrication Technology For Freeform Opticsmentioning

confidence: 99%

“…RFCML's honeycomb manufacturing creates some of the world's most powerful telescopes such as the 2 × 8.4 m Large Binocular Telescope (LBT) and the 25 m Giant Magellan Telescope (GMT). The first 8.4 m off-axis GMT segment was successfully completed to an accuracy of 19 nm root mean square (RMS) error in 2012 [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Fabrication and Dynamic Deflectometry Testing Methods for Freeform and Deformable Optics

Kim

Trumper

Choi

et al. 2017

Optical Design and Fabrication 2017 (Freeform, IODC, OFT)

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“…The first 8.4 m off-axis GMT segment was successfully completed to an accuracy of 19 nm root mean square (RMS) error in 2012. 3 In addition to its large size, the main challenge to manufacture the segments comes from the highly aspheric shape of the off-axis segments shown in Figure 1 (right). More than ~13 mm of aspheric departure requires customized metrology systems with complex null configurations and/or high dynamic range freeform metrology systems.…”

Section: Richard F Caris Mirror Lab Overviewmentioning

confidence: 99%