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A Study on the Improvement of Wavefront Sensing Accuracy for Shack-Hartmann Sensors

Shack-Hartmann 센서를 이용한 파면측정의 정확도 향상에 관한 연구

  • Roh, Kyung-Wan (Department of Safety Issue Research, Korea institute of Nuclear Safety) ;
  • Uhm, Tae-Kyoung (Department cf Mechanical Engineering, KAIST and Image Information Research Center) ;
  • Kim, Ji-Yeon (Department cf Mechanical Engineering, KAIST and Image Information Research Center) ;
  • Park, Sang-Hoon (Department cf Mechanical Engineering, KAIST and Image Information Research Center) ;
  • Youn, Sung-Kie (Department cf Mechanical Engineering, KAIST and Image Information Research Center) ;
  • Lee, Jun-Ho (Department of Optical Engineering, Kongju National University)
  • 노경완 (한국원자력안전기술원, 현안기술연구실) ;
  • 엄태경 (한국과학기술원 기계공학과, 영상정보특화연구센터) ;
  • 김지연 (한국과학기술원 기계공학과, 영상정보특화연구센터) ;
  • 박상훈 (한국과학기술원 기계공학과, 영상정보특화연구센터) ;
  • 윤성기 (한국과학기술원 기계공학과, 영상정보특화연구센터) ;
  • 이준호 (공주대학교 광공학과, 영상정보특화연구센터)
  • Published : 2006.10.25

Abstract

The SharkHartmann wavefront sensors are the most popular devices to measure wavefront in the field of adaptive optics. The Shack-Hartmann sensors measure the centroids of spot irradiance distribution formed by each corresponding micro-lens. The centroids are linearly proportional to the local mean slopes of the wavefront defined within the corresponding sub-aperture. The wavefront is then reconstructed from the evaluated local mean slopes. The uncertainty of the Shack-Hartmann sensor is caused by various factors including the detector noise, the limited size of the detector, the magnitude and profile of spot irradiance distribution, etc. This paper investigates the noise propagation in two major centroid evaluation algorithms through computer simulation; 1st order moments of the irradiance algorithms i.e. center of gravity algorithm, and correlation algorithm. First, the center of gravity algorithm is shown to have relatively large dependence on the magnitudes of noises and the shape & size of irradiance sidelobes, whose effects are also shown to be minimized by optimal thresholding. Second, the correlation algorithm is shown to be robust over those effects, while its measurement accuracy is vulnerable to the size variation of the reference spot. The investigation is finally confirmed by experimental measurements of defocus wavefront aberrations using a Shack-Hartmann sensor using those two algorithms.

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