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This work presents a method for detectors co-alignment in dual-channel spectrometer using optical coherence tomography. The method is proposed for the ELOIS (Enhanced Light Offner Imaging Spectrometer) developed by the AMOS company (Advance Mechanical and Optical Systems). This company designs and builds optical components and instruments related to the space industry and one of their current project is the ELOIS instrument. A crucial aspect in the development of the instrument is the correct alignment of the focal plane assembly components. During this phase, the two detectors of the spectrometer need to be correctly co-aligned with each other in the six degrees of freedom. This work presents a method using optical coherence tomography for the co-alignment of the detectors in tip, tilt and focus. The first part explains the theoretical aspects of optical coherence tomography and how it can be applied to the ELOIS instruments. The second part is the application of optical coherence tomography on a test bench replicating the components of the ELOIS. The procedure is detailed for this experimental test and an explanation of the results demonstrates the accuracy achievable with this method. The third part of this work explains the differences between the experimental test and the ELOIS instrument. The procedure of co-alignment and the achievable accuracy are detailed in the case of this specific dual-channel spectrometer.
Spectrometer --- Optical coherence tomography --- ELOIS --- Detectors alignement --- Focal plane assembly --- Experimental test --- Spectromètre --- Tomographie par coherence optique --- Alignement de détecteurs --- Plan focal --- Test expérimental --- Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique --- Ingénierie, informatique & technologie > Ingénierie aérospatiale
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This master thesis presents two instruments to determine the degree of linear polarization of au-roral light using Stokes parameters. Both instrumentation will focus on the three brightest linesof the visible spectrum:λ=427.8 nm,λ=577.7 nm andλ=630.0 nm. The first method uses atelescope to collect the light and a spectropolarimeter to disperse it. Optical devices are added tomanipulate the light and alter polarization before the spectropolarimeter. It has faced significantlow flux reception during previous missions that prevented to obtain accurate results. For that rea-son, a complete radiometric budget followed by a modelisation in CODE V of the light path wererealised to first quantify and then minimize these losses, mainly located at the exit of the telescopeand at the matcher of the spectropolarimeter. The outputs of this study allowed to increase thesignal-to-noise ratio of the detector. The second instrument directly selects the wavelength thanksto a set of two acousto-optic tunable filters, which replaces the function of the telescope and thespectropolarimeter. Experimental tests using laboratory lasers were run to calibrate and evaluatethe response of the instrument in frequency for each wavelength. This instrument has been usedin an auroral observation ground mission in Norway, which showed the good functioning of theinstrument. Unfortunately, the auroral light emission was poor in intensity and the results werenot enough convincing. As both instrumentation use different ways to diffract light, a comparisonof the two methods can be considered. Finally, an adaptation for more extreme conditions, suchas low temperature and pressure is presented at the end of this report.
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