Fabrication and testing of 1.4-m convex off-axis aspheric optical surfaces

Modern large telescopes such as TAO, LSST, TMT and EELT require 0.9m-4m monolithic convex secondary mirrors. The fabrication and testing of these large convex secondary mirrors of astronomical telescopes is getting challenging as the aperture of the mirror is getting bigger. The biggest challenge to fabricate these large convex aspheric mirrors is to measure the surface figure to a few nanometers, while maintaining the testing and fabrication cycle to be efficient to minimize the downtime. For the last a couple of decades there was huge advancement in the metrology and fabrication of large aspheric secondary mirrors. College of Optical Sciences in the University Arizona developed a full fabrication and metrology process with extremely high accuracy and efficiency for manufacturing the large convex secondary mirrors.In this paper modern metrology systems including Swing-Arm Optical Coordinate Measuring System (SOCMM) which is comparable to Interferometry and a Sub-aperture stitching interferometry scalable to a several meters have been presented. Also a Computer Controlled Fabrication Process which produces extremely fine surface figure and finish has been demonstrated. These most recent development has been applied to the fabrication and testing of 0.9m aspheric convex secondary mirror for the Tokyo Atacama Observatory's 6.5m telescope and the result has been presented.

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“…Due to the limitation of sensor and software only profile measurement was available and the accuracy was achieved to approximately 50nm RMS. 6 …”

Section: Swingarm Profilometer: 1997mentioning

confidence: 99%

Modern technologies of fabrication and testing of large convex secondary mirrors

Lowman

Dubin

et al. 2016

SPIE Proceedings

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“…With the ability of providing high image quality with few optical components, aspherical optics are widely used in modern optical systems, such as space telescopes, laser fusion systems, and lithography systems. In general, the specifications for the surface accuracy made on these aspherical components need to achieve nanometer-scale or even subnanometer-scale precision [4][5][6]. However, aspherical optics takes on a more complex shape compared with spherical optics, and conventional tools therefore cannot readily conform to the local varying curvatures [4,7,8].…”

Section: Introductionmentioning

confidence: 99%

“…In general, the specifications for the surface accuracy made on these aspherical components need to achieve nanometer-scale or even subnanometer-scale precision [4][5][6]. However, aspherical optics takes on a more complex shape compared with spherical optics, and conventional tools therefore cannot readily conform to the local varying curvatures [4,7,8]. Usually, small rigid tools and the manual method are typically employed to polish aspherical surfaces, but middle-to-high spatial frequency (MHSF) ripples and high-slope surface errors are often generated during these processes [6].…”

Section: Introductionmentioning

confidence: 99%

Rapid fabrication technique for nanometer-precision aspherical surfaces

et al. 2015

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High-precision aspherical optics are widely used in modern optical systems with the capability of providing high image quality, but an aspherical surface is more challenging to fabricate because of its more complex shape compared with other surfaces. Ion beam figuring (IBF) provides a highly deterministic technology for ultra-precision fabrication of aspherical surfaces. However, the convergent efficiency and final accuracy are strongly dependent on the original surface state, where the topography and distribution of the surface errors generated during the pre-processing should be taken into account. Consequently, we propose a combined technique that includes magnetorheological finishing, smoothing polishing, and IBF. This technique can effectively control different surface errors during the polishing process, and then rapidly impart nanometer-precision fabrication. Comparative figuring experiments are performed on a parabolic surface, and the original surfaces before IBF are pre-processed by manual polishing and our combined technique, respectively. The results indicate that abundant high-slope and middle-to-high frequency surface errors exist on the surface after conventional polishing, and this surface state limits the final fabrication accuracy. Nevertheless, a smooth surface is prepared by our combined technique and a nanometer-precision aspherical surface is rapidly obtained, which demonstrates the feasibility of our proposed method.

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“…Therefore, computer controlled optical surfacing (CCOS) processes have been developed for fabrication of precision optics since the 1960s [1][2][3][4][5]. These processes have radically different polishing mechanisms, including computer controlled polishing [6], ion beam figuring (IBF) [7], plasma-assisted chemical etching [8], magnetorheological finishing [9], magnetorheological jet polishing [10,11].…”

Section: Introductionmentioning

confidence: 99%

“…These processes have radically different polishing mechanisms, including computer controlled polishing [6], ion beam figuring (IBF) [7], plasma-assisted chemical etching [8], magnetorheological finishing [9], magnetorheological jet polishing [10,11]. Many large aspheric even off-axis segments have been successfully fabricated using them [4,5].…”

Section: Introductionmentioning

confidence: 99%

Investigation on tool function and removal characteristics for bonnet surfacing

Feng

Cheng

2015

MATEC Web of Conferences

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Abstract. Since computer controlled optical surfacing (CCOS) processes have been proposed in the 1960s, many processes are developed for precision optics successfully. In this present work, a novel approach, the precessions process, is proposed and used for large segments fabrication. The removal function of bonnet polisher based on velocity and pressure distribution, which are obtained from the geometry of the process tool-motion and Hertzian contact theory respectively, are simulated. A dynamic finite element analysis (FEA) model is constructed to optimize process parameters. At last, detailed experimental studies are carried out to verify the optimal parameters.

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Fabrication and testing of 1.4-m convex off-axis aspheric optical surfaces

Cited by 21 publications

References 9 publications

Modern technologies of fabrication and testing of large convex secondary mirrors

Modern technologies of fabrication and testing of large convex secondary mirrors

Rapid fabrication technique for nanometer-precision aspherical surfaces

Investigation on tool function and removal characteristics for bonnet surfacing

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