Digital Holographic Interferometry in the Long-Wave Infrared for the Testing of Large Aspheric Space Reflectors

Digital holographic (DH) interferometry has been developed in the long-wave infrared spectral range with CO2 lasers and microbolometer arrays. This application has been driven by the European Space Agency’s constant need of techniques for monitoring large displacements of large structures. Here the study focuses on the case of aspheric mirrors, like parabola and ellipses. Usually they are tested through interferometric wavefront error measurements which require expensive null-lenses matching each of the reflectors considered. In the case of monitoring deformation a holographic technique can be considered where the wavefront is compared with itself at different instant. Therefore the optical can be quite simple and easily reconfigurable from one reflector to another. The advantage of using long wavelength is that large deformations can be measured at once, in addition to being more immune against environmental perturbations. Another advantage of DH at such wavelengths is that the ratio between the wavelength and the pixel size allows reconstructing objects 5 to 10 times larger than with DH in the visible. In this project we considered first the case of a 1.1 meter diameter parabola for submillimeter range observations. Such specimen shows strong specular reflectivity. We have developed several set-ups with different ways to illuminate the object and to collect rays to form the object beam: either through point source or through and extended diffuser working by reflection of the laser beam. Both possibilities have been compared in terms of fringe quality as well as measurement range. We selected the diffuser illumination for applying the set-up into a large vacuum facility for measuring the deformation of the parabola between 224 and 107 K. Results of this measurement campaign are presented. A further application has been shown by observation of off-axis ellipse. In this case interferometric testing is difficult to achieve and LWIR DHI with diffuser illumination is found quite simple to implement and gives straightforward results.GSTP HOLODI

Détection de défauts dans des matériaux composites utilisés dans la constructions de planeurs, d'ULM et de coques de voiliers: Convention F.I.R.S.T. n° 2271

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Interactions cohérentes diffractives, du type courant chargé, de neutrinos et d'antineutrinos sur noyaux de Néon: Mémoire présenté en vue de l'obtentin du grade de licencié en sciences physiques -- Physique

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Détection de défauts dans les matériaux composites utilisés dans la construction de planeurs, d'ULM et de voiliers: Convention F.I.R.S.T. n° 2271

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Influence de la viscosité de surface sur les instabilités Marangoni-Bénard: Travail de fin d'études présenté en vue de l'obtention du grade d'ingénieur civil physicien -- Physique

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Analyse par PTV du champ de vitesse de surface dans l'instabilité de Marangoni-Bénard

L’expérience en microgravité BAMBI (Bifurcation Anomalies in Marangoni-Bénard Instabilities) a volé à bord du satellite FOTON-M2 en juin 2005. Pendant les 4 jours disponibles pour l’expérience, une couche d’huile de silicone (200 cSt) de 5 mm d’épaisseur et de 10x10cm de largeur, en contact avec une couche similaire d’hélium, a été soumise à une gamme de différences de température, afin d’y étudier en détail l’instabilité de Marangoni-Bénard menant à la formation spontanée de structures convectives hexagonales. Dans cette contribution, seul l’algorithme développé pour extraire les vitesses et trajectoires des particules dans le plan de l’interface est présenté, ainsi que les principaux résultats obtenus.info:eu-repo/semantics/publishe

Fluid physics experiments under microgravity conditions

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Long-wave infrared digital holography for the qualification of large space reflectors

Deformation metrology of complex and large space reflectors is a recurrent problem addressed by ESA. The challenging tasks of on-ground qualification and verification testing are to achieve the required accuracy in the measurement of these reflectors deformation and to verify their performance under simulated space conditions (vacuum, low temperature). A long-wave infrared digital holographic interferometer for the verification and validation of this type of reflector in a space environment is presented. It has been developed to fill the gap between holography/interferometry techniques in the visible wavelengths and methods based on structured light illumination like videogrammetry, stereocorrelation, and fringe/pattern projection. The former provide a good measurement uncertainty but the displacements are often too large to be measured and they require a very stable environment, while the latter provide large measurement range but with higher measurement uncertainty. The new instrument is based on digital holography and uses a CO2 lasers emitting at 10.6 µm combined with a commercial thermographic camera. A diffuser is illuminated by the laser beam, producing a speckle wavefront which is observed after reflection on the reflector surface. This reflected speckle wavefront behaves exactly as if the reflector was a diffusive surface, producing its own speckle, allowing the measurement of its deformation. The advantage of this configuration compared to a classical interferometer working at 10.6 µm, is that it requires no specific optics such as a null lens (in the case of parabola) or expensive illumination/collection optics (in the case of ellipse). The metrological certification of the system was performed in the laboratory by measuring the tilts of a 1.1 meter diameter parabolic reflector. The displacements are measured in parallel with a Doppler effect interferometer and the measurement uncertainty is estimated. The application of the new interferometer to the measurement of an elliptic reflector is also presented. The technique has been certified during a thermal-vacuum test. The deformation of the parabolic reflector is measured for a temperature variation from 288 K down to 113 K. The results are compared to previous results obtained on the same reflector with a high spatial resolution infrared interferometer, also developed at CSL

Telescience Operations at the Microgravity Research Center

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Nonlinear Convective Flows in a Laterally Heated Two-Layer System with a Temperature-Dependent Heat Release/Consumption at the Interface

Nonlinear convective flows developed under the joint action of buoyant and thermocapillary effects in a laterally heated two-layer system filling the closed cavity, have been investigated. The influence of a temperature-dependent interfacial heat release/consumption on nonlinear steady and oscillatory regimes, has been studied. It is shown that sufficiently strong temperature dependence of interfacial heat sinks and heat sources can change the sequence of bifurcations and lead to the development of specific oscillatory regimes in the system.SCOPUS: ar.jinfo:eu-repo/semantics/publishe