5 research outputs found
Active coherent beam combining and beam steering using a spatial mode multiplexer
Coherent beam combination is one promising way to overcome the power limit of
one single laser. In this paper, we use a Multi-Plane Light Converter to
combine 12 fibers at 1.03 micron with a phase locking setup. The overall loss
measurement gives a combination efficiency in the fundamental Hermite-Gaussian
mode as high as 70%. This setup can generate the fundamental and higher-order
Hermite-Gaussian modes and has beam steering capabilities
Experimental study of the role of trap symmetry in an atom-chip interferometer above the Bose-Einstein condensation threshold
We report the experimental study of an atom-chip interferometer using
ultracold rubidium 87 atoms above the Bose-Einstein condensation threshold. The
observed dependence of the contrast decay time with temperature and with the
degree of symmetry of the traps during the interferometer sequence is in good
agreement with theoretical predictions published in [Dupont-Nivet et al., NJP
18, 113012 (2016)]. These results pave the way for precision measurements with
trapped thermal atoms.Comment: 11 pages, 4 figure
Apport de l'optique non linéaire à l'imagerie infrarouge pour la détection de cibles à longue distance
There is a wide range of applications in active infrared detection technologies in defense and security. However, the limited range available by these systems limits their developments. Increasing sensors sensitivity is a key milestone to improve this range. Indeed, noise in infrared detectors is much higher than for visible detectors due to some physical and technological issues. The key idea of this manuscript is to use nonlinear optical technologies to convert the infrared signal to detect into the visible spectrum and use all the benefits of silicon based sensors. Recent advances in optical crystals and in pump laser regimes bring renewed interest to upconversion detection for some specific application cases identified in this thesis. A novel and easy method to improve the number of converted modes has been proposed after a careful study of multimode conversion both temporally and spatially. In order to give figures on detection improvement using upconversion, we conducted a theoretical and numerical study of the multimode conversion as well as two sets of experiments. The first one, using conversion in an OP-GaAs crystal and a monodetector addresses mid-infrared spectroscopy applications. The second one addresses active imaging applications for target recognition and identification in the near-infrared. By using a PPLN crystal, the near-infrared image is detected on a low noise CMOS camera. A key milestone of this work is the sensitivity improvement of such a detection. Sensitivities obtained in each experiment are one order of magnitude better than with direct detection using common infrared sensors.Les applications de dĂ©tection infrarouge active sont nombreuses dans le domaine de la dĂ©fense et la sĂ©curitĂ©. Cependant ces systĂšmes sont actuellement peu utilisĂ©s en pratique Ă cause de leur portĂ©e limitĂ©e. Un moyen dâaugmenter cette portĂ©e est dâamĂ©liorer la sensibilitĂ© des dĂ©tecteurs infrarouges qui possĂšdent des bruits bien plus Ă©levĂ©s que leurs Ă©quivalents dans le visible. LâidĂ©e principale de cette thĂšse est dâutiliser lâoptique non linĂ©aire pour effectuer une conversion de frĂ©quence du signal infrarouge Ă dĂ©tecter vers de plus basses longueurs dâondes et ainsi bĂ©nĂ©ficier des performances des dĂ©tecteurs fonctionnants Ă ces longueurs dâondes. Les dĂ©veloppements rĂ©cents en cristaux donnent un intĂ©rĂȘt nouveau Ă ces techniques pour certains cas applicatifs identifiĂ©s au cours de cette thĂšse. LâĂ©tude dĂ©taillĂ©e de la conversion multimode Ă la fois temporelle et spatiale, a permis de proposer une mĂ©thode simple et originale pour dĂ©passer lâĂ©tat de lâart en terme de nombre dâĂ©lĂ©ments rĂ©solus convertis. Pour quantifier prĂ©cisĂ©ment les avantages de ces conversions, une Ă©tude thĂ©orique et numĂ©rique de la conversion multimode a Ă©tĂ© menĂ©e et deux sĂ©ries dâexpĂ©riences ont Ă©tĂ© conduites. La premiĂšre concerne la dĂ©tection ponctuelle de signaux moyen-infrarouge pour des applications de spectroscopie par conversion dans un cristal dâOP-GaAs. La deuxiĂšme concerne la dĂ©tection de cibles par imagerie active dans le proche infrarouge par conversion dans un cristal de PPLN vers une camĂ©ra CMOS. Les performances en sensibilitĂ© obtenues sont dans les deux expĂ©riences meilleures dâun ordre de grandeur que les dĂ©tections directes avec les dĂ©tecteurs habituellement utilisĂ©s
Upconversion detection for long range active imaging in the infrared
Les applications de dĂ©tection infrarouge active sont nombreuses dans le domaine de la dĂ©fense et la sĂ©curitĂ©. Cependant ces systĂšmes sont actuellement peu utilisĂ©s en pratique Ă cause de leur portĂ©e limitĂ©e. Un moyen dâaugmenter cette portĂ©e est dâamĂ©liorer la sensibilitĂ© des dĂ©tecteurs infrarouges qui possĂšdent des bruits bien plus Ă©levĂ©s que leurs Ă©quivalents dans le visible. LâidĂ©e principale de cette thĂšse est dâutiliser lâoptique non linĂ©aire pour effectuer une conversion de frĂ©quence du signal infrarouge Ă dĂ©tecter vers de plus basses longueurs dâondes et ainsi bĂ©nĂ©ficier des performances des dĂ©tecteurs fonctionnants Ă ces longueurs dâondes. Les dĂ©veloppements rĂ©cents en cristaux donnent un intĂ©rĂȘt nouveau Ă ces techniques pour certains cas applicatifs identifiĂ©s au cours de cette thĂšse. LâĂ©tude dĂ©taillĂ©e de la conversion multimode Ă la fois temporelle et spatiale, a permis de proposer une mĂ©thode simple et originale pour dĂ©passer lâĂ©tat de lâart en terme de nombre dâĂ©lĂ©ments rĂ©solus convertis. Pour quantifier prĂ©cisĂ©ment les avantages de ces conversions, une Ă©tude thĂ©orique et numĂ©rique de la conversion multimode a Ă©tĂ© menĂ©e et deux sĂ©ries dâexpĂ©riences ont Ă©tĂ© conduites. La premiĂšre concerne la dĂ©tection ponctuelle de signaux moyen-infrarouge pour des applications de spectroscopie par conversion dans un cristal dâOP-GaAs. La deuxiĂšme concerne la dĂ©tection de cibles par imagerie active dans le proche infrarouge par conversion dans un cristal de PPLN vers une camĂ©ra CMOS. Les performances en sensibilitĂ© obtenues sont dans les deux expĂ©riences meilleures dâun ordre de grandeur que les dĂ©tections directes avec les dĂ©tecteurs habituellement utilisĂ©s.There is a wide range of applications in active infrared detection technologies in defense and security. However, the limited range available by these systems limits their developments. Increasing sensors sensitivity is a key milestone to improve this range. Indeed, noise in infrared detectors is much higher than for visible detectors due to some physical and technological issues. The key idea of this manuscript is to use nonlinear optical technologies to convert the infrared signal to detect into the visible spectrum and use all the benefits of silicon based sensors. Recent advances in optical crystals and in pump laser regimes bring renewed interest to upconversion detection for some specific application cases identified in this thesis. A novel and easy method to improve the number of converted modes has been proposed after a careful study of multimode conversion both temporally and spatially. In order to give figures on detection improvement using upconversion, we conducted a theoretical and numerical study of the multimode conversion as well as two sets of experiments. The first one, using conversion in an OP-GaAs crystal and a monodetector addresses mid-infrared spectroscopy applications. The second one addresses active imaging applications for target recognition and identification in the near-infrared. By using a PPLN crystal, the near-infrared image is detected on a low noise CMOS camera. A key milestone of this work is the sensitivity improvement of such a detection. Sensitivities obtained in each experiment are one order of magnitude better than with direct detection using common infrared sensors