Optical figuring specifications for thin shells to be used in adaptive telescope mirrors

Riccardi, Armando

doi:10.1117/12.673513

Cited by 4 publications

(9 citation statements)

References 3 publications

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“…Regardless their origin, the correction of these mid frequency features requires a smoothing process. The value of surface RMS error achieved after bonnet polishing is close to the figuring specification expected for a glass shell before any error compensation by the actuators (flattening) in the framework of an adaptive/active system [19]. We achieved the 15 nm RMS error by polishing the thin shell glued on the stiffening holder, where it was displaying the surface error map of Fig.3A with initial RMS (PV) error of 106 nm (527 nm).…”

Section: Bonnet Polishing Of the Thin Glass Shellsupporting

confidence: 70%

Thin glass shells for active optics for future space telescopes

et al. 2019

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We present a method for the manufacturing of thin shells of glass, which appears promising for the development of active optics for future space telescopes. The method exploits the synergy of different mature technologies, while leveraging the commercial availability of large, high-quality sheets of glass, with thickness up to few millimeters. The first step of the method foresees the pre-shaping of flat substrates of glass by replicating the accurate shape of a mold via hot slumping technology. The replication concept is advantageous for making large optics composed of many identical or similar segments. After the hot slumping, the shape error residual on the optical surface is addressed by applying a deterministic sub-aperture technology as computer-controlled bonnet polishing and/or ion beam figuring. Here we focus on the bonnet polishing case, during which the thin, deformable substrate of glass is temporary stiffened by a removable holder. In this paper, we report on the results so far achieved on a 130 mm glass shell case study.

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Section: Bonnet Polishing Of the Thin Glass Shellsupporting

confidence: 70%

Thin glass shells for active optics for future space telescopes

et al. 2019

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“…After cooling down of the shell-mold system, the slumped glass shell is released from the mold. The results were encouraging but displaying an error still too high compared to the requirements: we achieved a surface Root Mean Square (RMS) error >100 nm versus a requirement <10 nm over 100 mm spatial scale [12]. In the present study, we focus on a simple case, namely, shells made in BOROFLOAT® 33 glass, 130 mm wide and 2 mm thick.…”

Section: Icso 2018 International Conference On Space Opticsmentioning

confidence: 85%

Manufacturing of thin glass shells for future space telescopes

Vecchi

Basso

Civitani

et al. 2019

International Conference on Space Optics — ICSO 2018

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We present a method for the manufacturing of thin shells of glass, which appears promising for the production of lightweight mirrors for future space telescopes. The method exploits the synergy of different mature technologies, while it takes advantage of the commercial availability of large, high-quality sheets of glass, with thickness up to few millimeters. The first step of the method foresees the pre-shaping of flat substrates of glass by replicating the accurate shape of a mold via hot slumping technology. The replication concept can be strongly beneficial for making large optics composed of many identical or similar segments. After the hot slumping, the shape error residual on the optical surface is addressed by applying a deterministic sub-aperture technology as computer-controlled bonnet polishing and/or ion beam figuring. Here we focus on the bonnet polishing case, during which the thin, deformable substrate of glass is temporary stiffened by a removable holder. In this paper, we report on the latest results achieved on a 130 mm glass shell case study.

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“…4, the relation between the position command vector c and the actuator position vector p is given by (12) …”

Section: Actuator Coupling and Fitting Errormentioning

confidence: 99%

“…Considering Eqs. (2) and (12), the relationship between a generic shell deformation z and the command vector c is given by The least-square fitting of a generic wave-front w can be obtained as…”

Section: Actuator Coupling and Fitting Errormentioning

confidence: 99%

Fitting error analysis for the VLT deformable secondary mirror

Riccardi¹,

Xompero

Busoni

2006

SPIE Proceedings

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The present work reports the results of fitting error analysis for the Deformable Secondary Mirrors (DSM) of the Very Large Telescope (VLT). The analysis is performed in terms of residual rms wave-front error, PSF profile, requested actuator position and force stroke. A comparison with an ideal Karhunen-Loève and Zernike wave-front correctors is also shown. The analysis is based on influence functions simulated by FEA. The new generation of Adaptive Optics at VLT includes the development of a Deformable Secondary Mirror [1] (DSM, aka Adaptive Secondary Mirror). The unit is being designed by an Italian consortium composed of Microgate (Bolzano), ADS Int. (Lecco) and the INAF-Osservatorio Astrofisico di Arcetri. This device represents the third generation of DSM technology, following the MMT (336-actuators, currently operating [2]) and the LBT (672-actuators, currently in assembly phase [3]) units.A feasibility study for the DSM has been completed in August 2005 and a contract has been signed with the same contractors for preliminary and final design.The adaptive surface is a 2.0mm-thick Zerodur shell that is deformed by electromagnetic (voice-coil like) force actuators. Internal metrology made of co-located capacitive sensors allows to control the actuator force to move to or keep the commanded mirror shape.The present paper analyzes the effectiveness of matching the commanded shape to typical wavefront distortion induced by atmospheric turbulence (fitting error) as a function of the number of corrected modes. Because DSM actuators are force actuators, this parameter is also computed to check that no excess of force is applied to keep the dissipation budget in reasonable limits. Moreover the performance degradation with respect to the number of not working actuators is computed. The residual fitting error of large stroke and low-order Zernike modes is also analyzed to assure active optics capabilities and ranges.

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Optical figuring specifications for thin shells to be used in adaptive telescope mirrors

Cited by 4 publications

References 3 publications

Thin glass shells for active optics for future space telescopes

Thin glass shells for active optics for future space telescopes

Manufacturing of thin glass shells for future space telescopes

Fitting error analysis for the VLT deformable secondary mirror

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