Korean Journal of Optics and Photonics (한국광학회지)

Optical Society of Korea (한국광학회)
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Testing of a Convex Aspheric Secondary Mirror for the Cassegrain Telescope

카세그레인 망원경의 볼록비구면 반사경 파면오차 측정

  • Kim, Goeun (Science of Measurement, University of Science and Technology) ;
  • Rhee, Hyug-Gyo (Science of Measurement, University of Science and Technology) ;
  • Yang, Ho-Soon (Science of Measurement, University of Science and Technology)
  • 김고은 (과학기술연합대학원대학교 측정과학과) ;
  • 이혁교 (과학기술연합대학원대학교 측정과학과) ;
  • 양호순 (과학기술연합대학원대학교 측정과학과)
  • Received : 2017.10.31
  • Accepted : 2017.11.09
  • Published : 2017.12.25
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Abstract

The Cassegrain telescope consists of a primary concave mirror and a secondary convex mirror. In the case of a secondary mirror, it is more difficult to test wavefront error than for a primary mirror, because it reflects the entire testing beam, as it is convex in shape. In this paper we tested the wavefront error of a complex aspheric convex secondary mirror by using the Simpson-Oland-Meckel Hindle test. To separate the systematic errors, such as fabrication error and alignment error of a meniscus lens, we adopted the QN absolute test (pixel-based absolute test using the quasi-Newton method) as well. Finally, we compared the measured result with that of an ASI (Aspheric Stitching Interferometer) made by the QED company, which resulted in an rms difference of only 2.5 nm, showing a similar shape of astigmatism aberration.

카세그레인 망원경은 오목한 주경과 볼록한 부경으로 이루어져있다. 특히 부경의 경우 크기는 작지만 볼록한 형태로 빛을 모두 퍼트려 파면오차 측정이 어렵다. 본 논문에서는 비구면 계수가 여러 개인 볼록비구면 반사경의 파면오차를 Simpson-Oland-Meckel (SOM) 힌들 테스트를 적용하여 측정하였다. 그리고 실험 구성에서 발생하는 계통오차를 분리해내기 위해 QN 절대측정법을 추가로 적용함으로써 힌들 렌즈 제작 및 정렬 오차를 포함한 계통오차를 보정하고 볼록비구면 반사경만의 파면오차를 구하였다. 이렇게 구한 볼록비구면 반사경의 파면오차와 QED사의 ASI (Aspheric Stitching Interferometer)로 측정한 파면오차와 비교한 결과, 모두 $45^{\circ}$ 방향의 비점수차 형태를 가지며 rms 값의 차이가 약 2.5 nm rms 이내로 매우 작음을 확인하였다.

Keywords

References

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