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Theses

Développement de télémètres laser de haute exactitude et de haute résolution pour applications spatiales

Abstract : Improving the angular resolution of telescopes implies an increase of their size. Spacecrafts in formation flying are more and more investigated for future space telescope projects. Operation of such systems requires absolute distance measurement between two spacecrafts with an accuracy of few tens of microns. The absolute distance measurement with high precision is also at the centre of fundamental physic experiments. My thesis work has consisted in the development of two rangefinders, T2M and Iliade which could be used for these projects. The difficulty is to combine a great measurement range with high sensitivity in a simple set-up for being eventually embedded instruments. Our goal is to measure a distance of one kilometre with an accuracy better than one micron. The difference between T2M and Iliade resides in their designs but also in their complexity and their resolution. The T2M rangefinder uses the phase difference of a beam modulated in amplitude and split in a measurement path and a reference path. The target resolution with this system is in the tens of nanometres. T2M is able to reach a high accuracy because the distance is obtained from frequency measurements. Cyclic errors linked to the use of phase comparison are suppressed using an optical switching system which exchanges the beams of the two paths with respect to the two detection chains. After having stabilized the frequency of the beatnote between the two laser, I have worked on the improvement of the resolution. I have also worked on the suppression of different errors which affect the accuracy of T2M. Objectives seem to be reached and the results are very encouraging for the future tests and developments. The Iliade rangefinder combines a time of flight measurement between optical pulses and a two-wavelength interferometric measurement. This sophisticated system compared to T2M, is expected to have a resolution below one nanometer. I have characterised the 20 GHz pulse source and shown that the 65 fs timing jitter is mainly limited by the phase noise of the initial two-mode beat-note. I have worked on a fibered Fabry Perot cavity for single-mode laser frequency pre-stabilization and demonstrated a scheme for obtaining a dispersive-shaped error signal without any modulation. I have studied a numerical method based on harmonic analysis in order to measure phase difference with an accuracy better than 10-5 radian. The Iliade rangefinder is presently under development.
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Submitted on : Friday, April 15, 2011 - 1:27:13 PM
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Clément Courde. Développement de télémètres laser de haute exactitude et de haute résolution pour applications spatiales. Physique [physics]. Université Nice Sophia Antipolis, 2011. Français. ⟨tel-00586258⟩

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