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Laser guide star defocus measurement and control with a four quadrant sensor
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Today bigger and bigger telescopes are being built, as astronomers want to reach further out in space surrounding the Earth. Bigger telescopes are not always better since the atmosphere distorts the light coming from stars and other celestial bodies and the images will be blurred. One way to minimise the effects from the atmosphere is to use adaptive optics, and in most cases a curvature wavefront sensor is used. The main concern of this thesis was to investigate whether it is possible to achieve better results using a tip-tilt sensor compared to using a curvature wavefront sensor. Comparisons were also made with a curvature wavefront sensor measuring only tip-tilt. Tip and tilt are Zernike polynomials. A study, with the purpose of finding good simulation parameters, was made as well as an investigation how the height-shift of the sodium layer influences the focus of the telescope. The investigations trying to find the ideal value of the loop gain lead to the value 0.5. The loop gain is of less importance for bright stars, but seems to be rather important when simulating fainter star such as stars with magnitude 18. Due to the long simulation times required to simulate a 2 seconds observation, it was not possible to finish the investigation whether STRAP, the tip-tilt sensor, is better to use than the curvature wavefront sensor.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Adaptiv Optik
Keyword [sv]
URN: urn:nbn:se:ltu:diva-55449ISRN: LTU-EX--01/357--SELocal ID: c4f6c9c2-90db-49e8-a954-b1676d0d39fbOAI: diva2:1028831
Subject / course
Student thesis, at least 30 credits
Educational program
Engineering Physics, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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