Computation of misalignment and primary mirror astigmatism figure error of two-mirror telescopes

Zhiyuan Gu; Yang Wang; Guohao Ju; Changxiang Yan

doi:10.1117/1.JATIS.4.1.019002

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28 February 2018 Computation of misalignment and primary mirror astigmatism figure error of two-mirror telescopes

Zhiyuan Gu, Yang Wang, Guohao Ju, Changxiang Yan

J. of Astronomical Telescopes, Instruments, and Systems, 4(1), 019002 (2018). https://doi.org/10.1117/1.JATIS.4.1.019002

Abstract

Active optics usually uses the computation models based on numerical methods to correct misalignments and figure errors at present. These methods can hardly lead to any insight into the aberration field dependencies that arise in the presence of the misalignments. An analytical alignment model based on third-order nodal aberration theory is presented for this problem, which can be utilized to compute the primary mirror astigmatic figure error and misalignments for two-mirror telescopes. Alignment simulations are conducted for an R-C telescope based on this analytical alignment model. It is shown that in the absence of wavefront measurement errors, wavefront measurements at only two field points are enough, and the correction process can be completed with only one alignment action. In the presence of wavefront measurement errors, increasing the number of field points for wavefront measurements can enhance the robustness of the alignment model. Monte Carlo simulation shows that, when −2 mm ≤ linear misalignment ≤ 2 mm, −0.1 deg ≤ angular misalignment ≤ 0.1 deg, and −0.2 λ ≤ astigmatism figure error (expressed as fringe Zernike coefficients C₅ / C₆, λ = 632.8 nm) ≤0.2 λ, the misaligned systems can be corrected to be close to nominal state without wavefront testing error. In addition, the root mean square deviation of RMS wavefront error of all the misaligned samples after being corrected is linearly related to wavefront testing error.

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Zhiyuan Gu, Yang Wang, Guohao Ju, and Changxiang Yan "Computation of misalignment and primary mirror astigmatism figure error of two-mirror telescopes," Journal of Astronomical Telescopes, Instruments, and Systems 4(1), 019002 (28 February 2018). https://doi.org/10.1117/1.JATIS.4.1.019002

Received: 21 September 2017; Accepted: 5 February 2018; Published: 28 February 2018

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