Active optics in modern large optical telescopes

Noethe, L.

doi:10.1016/s0079-6638(02)80025-7

Cited by 44 publications

(24 citation statements)

References 30 publications

(34 reference statements)

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“…7 One would be a regular geometry with hexagonal symmetry where neighboring supports form equal lateral triangles. However, the symmetry is incompatible with the circular shape of the mirror.…”

Section: Mathematical Form Of the Axial Support Optimization Of Wfstmentioning

confidence: 99%

“…2 This general problem is an interesting topic. [3][4][5][6][7][8][9][10][11][12][13][14] In the past, researchers were only able to make a rough estimate of the numbers and optimum locations of the support points based on the theory of deflections of thin plates. 1,[3][4][5]11 In the last decade, based on finite element method (FEM), structural optimization technology is used to design support of astronomical telescopes.…”

Section: Introductionmentioning

confidence: 99%

“…1,[3][4][5]11 In the last decade, based on finite element method (FEM), structural optimization technology is used to design support of astronomical telescopes. [6][7][8][9]12,13 The term structural optimization was initially used for the optimization of engineering structures, such as buildings, automobiles, or airplane structures for improved strength or stiffness properties and reduced weight or cost. 15 Before computer-based optimization became widely used, structural components, such as beams and plates, were optimized using the calculus of variations.…”

Section: Introductionmentioning

confidence: 99%

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Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope

et al. 2016

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Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope," Opt. Eng. 55(3), 035105 (2016), Abstract. The optimization of a primary mirror support system is one of the most critical problems in the design of large telescopes. Here, we propose a hybrid optimization methodology of variable densities mesh model (HOMVDMM) for the axial supporting design, which has three key steps: (1) creating a variable densities mesh model, which will partition the mirror into several sparse mesh areas and several dense mesh areas;(2) global optimization based on the zero-order optimization method for the support of primary mirror with a large tolerance; (3) based on the optimization results of the second step, further optimization with first-order optimization method in dense mesh areas by a small tolerance. HOMVDMM exploits the complementary merits of both the zero-and first-order optimizations, with the former in global scale and the latter in small scale. As an application, the axial support of the primary mirror of the 2.5-m wide-field survey telescope (WFST) is optimized by HOMVDMM. These three designs are obtained via a comparative study of different supporting points including 27 supporting points, 39 supporting points, and 54 supporting points. Their residual half-path length errors are 28. 78, 9.32, and 5.29 nm. The latter two designs both meet the specification of WFST. In each of the three designs, a global optimization value with high accuracy will be obtained in an hour on an ordinary PC. As the results suggest, the overall performance of HOMVDMM is superior to the first-order optimization method as well as the zero-order optimization method.

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Section: Mathematical Form Of the Axial Support Optimization Of Wfstmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope

et al. 2016

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“…They are also the ones which appear statistically with the largest amplitudes in an expansion of the misalignment error due to random signal noise. In modern large active optical telescopes [2] containing both segmented and flexible monolithic mirrors the lowest normal modes could largely be compensated or corrected by other elements in the telescope optics. This shows the need to compare the normal modes with other sets of modes used in large telescopes, for example Zernike polynomials or elastic modes of monolithic mirrors [3].…”

Section: Introductionmentioning

confidence: 99%

Analytical expressions for optimum alignment modes of highly segmented mirrors

Noethe¹

2005

Journal of Modern Optics

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Abstract. The major sources causing deterioration of optical quality in extremely large optical telescopes are misadjustments of the mirrors, deformations of monolithic mirrors, and misalignments of segments in segmented mirrors. For active optics corrections, all three errors, which can partially compensate each other, are measured simultaneously. It is therefore of interest to understand the similarities and differences between the three corresponding types of modes which describe these errors. The first two types are best represented by Zernike polynomials and elastic modes respectively, both of them being continuous and smooth functions. The segment misaligment modes, which are derived by singular value decomposition, are by their nature not smooth and in general discontinuous. However, for mirrors with a large number of segments, the lowest modes become effectively both smooth and continuous. This paper derives analytical expressions for these modes, using differential operators and their adjoints, for the limit case of infinitesimally small segments. For segmented mirrors with approximately 1000 segments, it is shown that these modes agree well with the corresponding lowest singular value decomposition modes. Furthermore, the analytical expressions reveal the nature of the segment misalignment modes and allow for a detailed comparison with the elastic modes of monolithic mirrors. Some mathematical features emerge as identical in the two cases.

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“…Flexures have a distinct advantage in that they do not generate backlash. Furthermore, a position sensor is used to provide feedback for controlling position and stiffness [6].…”

Section: Celt Telescopementioning

confidence: 99%

Sparse Aperture Speckle Interferometry Telescope Active Optics Control System

Clause¹

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Sparse Aperture Speckle Interferometry Telescope Active Optics Control SystemMatthew Clause A conventional large aperture telescope required for binary star research is typically cost prohibitive. A prototype active optics system was created and fitted to a telescope frame using relatively low cost components. The active optics system was capable of tipping, tilting, and elevating the mirrors to align reflected star light. The low cost mirror position actuators have a resolution of 31 nm, repeatable to within 16 nm. This is accurate enough to perform speckle analysis for the visible light spectrum. The mirrors used in testing were not supported with a whiffletree and produced trefoil-like aberrations which made phasing two mirrors difficult. The active optics system was able to successfully focus and align the mirrors through manual adjustment. Interference patterns could not be found due to having no method of measuring the mirror surfaces, preventing proper mirror alignment and phasing. Interference from air turbulence and trefoil-like aberrations further complicated this task. With some future project additions, this system has the potential to be completely automated. The success of the active optics actuators makes for a significant step towards a fully automated sparse aperture telescope.

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Active optics in modern large optical telescopes

Cited by 44 publications

References 30 publications

Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope

Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope

Analytical expressions for optimum alignment modes of highly segmented mirrors

Sparse Aperture Speckle Interferometry Telescope Active Optics Control System

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