Precessions process for efficient production of aspheric optics for large telescopes and their instrumentation

Walker, David D.; Beaucamp, Anthony; Bingham, R. G.; Brooks, D.; Freeman, R. R.; Kim, Sowoon; King, Andrew; McCavana, Gerry; Morton, R.; Riley, David R.; Simms, J.

doi:10.1117/12.456677

Cited by 50 publications

(29 citation statements)

References 7 publications

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“…Manufacturing errors of 5 arcsec are in line with expected optical performances achievable with the previous manufacturing process [10] that was based on the bonnet polishing of the shell with a IRP600 Zeeko machine [12] combined with a pitch tool directly mounted on its vertical carriage, without any final correction via IBF. The achieved results with a manufactured prototypal shell have been 17 arcsec HEW on axis (as measured with X-rays in full illumination at the Panter/MPE facility).…”

Section: The Optical Designmentioning

confidence: 91%

Thin fused silica optics for a few arcsec angular resolution and large collecting area x-ray telescope

et al. 2013

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The implementation of a X-ray mission with high imaging capabilities, similar to those achieved with Chandra (< 1 arcsec Half Energy Width, HEW), but with a much larger throughput is a very attractive perspective, even if challenging. For such a mission the scientific opportunities, in particular for the study of the early Universe, would remain at the state of the art for the next decades. At the beginning of the new millennium the XEUS mission has been proposed, with an effective area of several m 2 and an angular resolution better than 2 arcsec HEW. Unfortunately, after the initial study, this mission was not implemented, mainly due to the costs and the low level of technology readiness. Currently the most advanced proposal for such a kind of mission is the SMART-X project, led by CfA and involving several other US Institutes. This project is based on adjustable segments of thin foil mirrors with piezo-electric actuators, aiming to achieve an effective area > 2 m 2 at 1 keV and an angular resolution better than 1 arcsec HEW. Another attractive technology to realize an X-ray telescope with similar characteristics is being developed at NASA/Goddard. In this case the mirrors are based on Si substrates that are super-polished and figured starting from a bulky Si ingot, from which they are properly cut. Here we propose an alternative method based on precise direct grinding, figuring and polishing of thin (a few mm) glass shells with innovative deterministic polishing methods. This is followed by a final correction via ion figuring to obtain the desired accuracy in order to achieve the 1 arc sec HEW requirement. For this purpose, a temporary stiffening structure is used to support the shell from the polishing operations up to its integration in the telescope supporting structure. We will present the technological process under development, the results achieved so far and some mission scenarios based on this kind of optics, aiming to achieve an effective area more than 10 times larger than Chandra and an angular resolution of 1 arcsec HEW on axis and of a few arcsec off-axis across a large field of view (1 deg in diameter).

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Section: The Optical Designmentioning

confidence: 91%

Thin fused silica optics for a few arcsec angular resolution and large collecting area x-ray telescope

et al. 2013

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“…Various stages in the development of the Precessions TM polishing process have been reported elsewhere 1,2,3,4,5,6,7,8 . In summary it is an automated polishing process, based on precise CNC control of the position and orientation of a spinning, inflated, membrane-tool with respect to the part's surface.…”

Section: Introductionmentioning

confidence: 98%

New results from the Precessions polishing process scaled to larger sizes

Walker

Beaucamp

Brooks

et al. 2004

Optical Fabrication, Metrology, and Material Advancements for Telescopes

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The Precessions process uses an inflated membrane-tool that delivers near-Gaussian polishing spots. The toolmotion over the part can be constructed to preserve an aspheric form whilst removing damage from preceding processes, or control the form through a tool-path prescribed by numerical optimization. The process has previously been validated on surfaces up to 200mm diameter and used extensively in industrial environments. In this paper we report the first trials on a substantially larger part -a 500mm diameter f/1 ellipsoidal mirror -as part of the UK's technology-development for Extremely Large Telescopes. We draw attention to subtle problems that have arisen along the way. We also report on developing the process for free-form surfaces, in contrast to the axially-symmetric parts worked hitherto. The paper concludes with an assessment of the lessons learnt from the experiments, as they may impact on realization in a practical ELT segment fabrication facility.

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“…[1][2][3][4][5][6][7][8][9] ) at various stages during its development. We summarize the operation of the process as follows.…”

Section: Introductionmentioning

confidence: 99%

New developments in the precessions process for manufacturing free-form, large-optical, and precision-mechanical surfaces

et al. 2006

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The recent upsurge in the demand for off-axis and complex "freeform" optical surfaces is driving the development of novel processes for their fabrication. This paper focuses on recent developments of the Precessions CNC polishing process for freeform surfaces, including off-axis as a special case. First, the surface-prescription and metrology-data, and their relation to the data-input for the polishing machines, are considered. The relevance of consistent coordinate frames is emphasised. An outline of how the process can 'polish' a ground freeform part (improve the texture), and then 'figure' the part (reduce the form errors) is given. Specific experimental case-studies are then presented, illustrating the versatility of the process on different materials and forms.Recent work is included in which the process-speed has been moderated in order to remove tens of nanometres of stock material, rather then the more usual hundreds of nanometres to tens of microns as in the standard Precessions process. The relevance of this to improving the ultimate surface-precision that should be achievable by this method is described. As a final illustration, the potential of the process to the rapid fabrication of the hundreds to thousands of 1-2 metre class mirror segments required for extremely large telescopes is considered.

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Precessions process for efficient production of aspheric optics for large telescopes and their instrumentation

Cited by 50 publications

References 7 publications

Thin fused silica optics for a few arcsec angular resolution and large collecting area x-ray telescope

Thin fused silica optics for a few arcsec angular resolution and large collecting area x-ray telescope

New results from the Precessions polishing process scaled to larger sizes

New developments in the precessions process for manufacturing free-form, large-optical, and precision-mechanical surfaces

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