CGH for ESO’s ELT M2 reference plate: fabrication of high precision CGHs

Burmeister, Frank; Ehrhardt, Sascha; Benkenstein, Tino; Lammers, Tom; Klein, Antonia C.; Schleicher, Philipp; Flügel-Paul, Thomas; Zeitner, Uwe D.; Giraud, Philémon; Makhlouf, Houssine; Mercier-Ythier, Renaud; Cluzel, R.; Harel, Emmanuelle

doi:10.1117/12.2562827

Cited by 5 publications

(4 citation statements)

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“…An optical test bench was specifically built with the only purpose of polishing the reference surface. This test bench includes a vibration insensitive interferometer and a large CGH ( [7] and [8]). ESO requested to double check the spherical aberration of the test plate with an accuracy better than 300 nm rms WFE.…”

Section: Figure : Elt M2 Aspheric Sector Reference Platementioning

confidence: 99%

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Development of an interferometric test bench for the manufacturing of the ELT secondary mirror

Mercier-Ythier,

Monin,

Foucaud

et al. 2024

Optical Fabrication and Testing VIII

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Safran Reosc was awarded the manufacturing of the Secondary Mirror of the Extremely Large Telescope by ESO in 2016. The secondary mirror is a 4-meter convex mirror, the world's largest convex precision mirror ever made. As of spring 2024, this mirror is in its final phase of polishing. It is regularly controlled on a dedicated interferometric test bench (ITB) specifically designed to achieve the best accuracy on such a large mirror. The test bench was thoroughly validated in September 2023 and all its requirements were demonstrated. This bench includes a convex-concave test plate together with a unique custom interferometer system, both specifically designed and manufactured for this test bench. In fact, the specific requirements of this very large mirror forbid the use of off-the-shelf component or interferometer and it was necessary to design a specific interferometer to cope with all the requirements. Furthermore, it was necessary to manufacture an almost perfect 2-m reference plate to control the mirror. It took about 3 years to manufacture this reference plate with the requested accuracy.The test bench makes a measurement on 24 sub-pupils which are stitched together to reconstruct the final surface error. The full aperture measurement and the map stitching lasts around 2 hours. Specific sensors are used to monitor the stitching process and the stitching algorithm had to be adapted in order to fulfil the stringent performance requirements.In this paper, we present the main features of the bench, the alignment strategy, the test results obtained on the bench and the stitching algorithm developed to reconstruct the surface error.

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Section: Figure : Elt M2 Aspheric Sector Reference Platementioning

confidence: 99%

“…The total error budget for this CGH was a maximum WFE of 7.2 nm rms double-pass. IOF implemented specific calibrations to achieve this error budget ( [8]). The second CGH was manufactured on a smaller substrate for the crosscheck purpose.…”

Section: Figure : Elt M2 Aspheric Sector Reference Platementioning

confidence: 99%

Development of an interferometric test bench for the manufacturing of the ELT secondary mirror

Mercier-Ythier,

Monin,

Foucaud

et al. 2024

Optical Fabrication and Testing VIII

View full text Add to dashboard Cite

show abstract

“…An example of extreme requirements onto the accuracy of the test CGH is the secondary mirror of ESO's Extremely Large Telescope [13]. Due to its convex shape, the 4.2m diameter secondary mirror could not be directly characterized using a CGH but is tested during the fabrication process using a refractive aspheric reference plate.…”

Section: Computer-generated Holograms For Asphere Testing Of Telescop...mentioning

confidence: 99%

The potential of e-beam lithography for micro- and nano-optics on large areas

Zeitner

Banasch

Trost

2023

Novel Patterning Technologies 2023

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The availability of high-resolution and high throughput lithographic fabrication technologies such as electron-beam lithography based on Variable Shaped Beam writing and Character Projection opens the way for the flexible use of various optical nano-structures for some of the most demanding applications. The paper discusses the technical features, advantages, and limitations of these pattering approaches and will show how they can favorably be combined to realize optical nano-structures for applications, which are as diverse as gratings for ultra-short laser pulses or high resolution spectrometers, computer generated holograms for asphere testing, various optical meta-structures (lenses, gratings), or UV-polarizers.

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“…An example of extreme requirements on the accuracy of the test CGH is the secondary mirror of ESO's Extremely Large Telescope. 13 Due to its convex shape, the 4.2 m diameter secondary mirror could not be directly characterized using a CGH but is tested during the fabrication process using a refractive aspheric reference plate. The CGH for the characterization of this reference plate was fabricated by Fraunhofer IOF using the e-beam lithographic processes as described above.…”

Section: Examples Of E-beam Written Nano-optical Elementsmentioning

confidence: 99%

Potential of E-beam lithography for micro- and nano-optics fabrication on large areas

Zeitner

Banasch

Trost

2023

J. Micro/Nanopattern. Mats. Metro.

Self Cite

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.The availability of high-resolution and high-throughput lithographic fabrication technologies, such as electron-beam lithography, based on variable shaped beam writing and character projection opens the way for the flexible use of various optical nano-structures for some of the most demanding applications. We discuss the technical features, advantages, and limitations of these pattering approaches and show how they can favorably be combined to realize optical nano-structures for applications, which are as diverse as gratings for ultra-short laser pulses or high-resolution spectrometers, computer generated holograms for asphere testing, various optical meta-structures (lenses and gratings), or UV-polarizers.

show abstract

CGH for ESO’s ELT M2 reference plate: fabrication of high precision CGHs

Cited by 5 publications

References 0 publications

Development of an interferometric test bench for the manufacturing of the ELT secondary mirror

Development of an interferometric test bench for the manufacturing of the ELT secondary mirror

The potential of e-beam lithography for micro- and nano-optics on large areas

Potential of E-beam lithography for micro- and nano-optics fabrication on large areas

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