References of "Dubois, Frank"
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See detailLong-wave infrared digital holographic interferometry with diffuser or point source illuminations for measuring deformations of aspheric mirrors
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Queeckers, Patrick et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2014), 53(11), 112309

Long-wave infrared digital holographic interferometry with CO2 laser and microbolometer arrays has been developed for testing the large deformations of space reflectors. The setup considered is a ... [more ▼]

Long-wave infrared digital holographic interferometry with CO2 laser and microbolometer arrays has been developed for testing the large deformations of space reflectors. The setup considered is a Mach–Zehnder, associated to the digital holography reconstruction of the wavefront in the inline configuration with phase shifting. Two possibilities exist for illuminating the tested reflector: either with a point source (similarly to classical interferometry) or an extended source (with a diffuser). This paper presents the development of a modular setup which allows comparing both in the case of a parabolic mirror [less ▲]

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See detailDigital Holographic Interferometry in the Long-Wave Infrared for the Testing of Large Aspheric Space Reflectors
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Stockman, Yvan ULg et al

in Osten, Wolfgang (Ed.) Fringe 2013 (2014)

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 ... [more ▼]

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. [less ▲]

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See detailDigital Holographic Interferometry with CO2 Lasers Applied to Aspheric Space Reflectors Testing
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

Conference (2013, May)

Digital holographic interferometry at long infrared wavelengths allows monitoring large deformations of space reflectors during vacuum-thermal testing. We present different optical schemes and an ... [more ▼]

Digital holographic interferometry at long infrared wavelengths allows monitoring large deformations of space reflectors during vacuum-thermal testing. We present different optical schemes and an application to the complex case of elliptic reflector. [less ▲]

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See detailDigital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflectors metrology
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

in Applied Optics (2013), 52(1), 102-116

Digital holographic interferometry in the long wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements which ... [more ▼]

Digital holographic interferometry in the long wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test. [less ▲]

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See detailDigital Holographic Interferometry and ESPI at Long Infrared Wavelengths with CO2 Laser (invited paper)
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

in Digital Holography and 3D Imaging (DH2012) (2012, April 28)

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See detailDevelopment of digital holography in the long wave infrared range for assessment of space reflectors
Thizy, Cédric ULg; Vandenrijt, Jean-François ULg; Georges, Marc ULg et al

in Proceedings of ICSO 2010 - International Conference on Space Optics (2010, October)

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See detailDisplacement measurements of a parabolic reflector by holographic interferometry in the long-wavelength infrared
Vandenrijt, Jean-François ULg; Georges, Marc ULg; Thizy, Cédric ULg et al

in International Astronautical Congress 2010 (2010, September)

Deformation metrology of complex shape space structure and reflectors is a recurrent problem addressed by ESA. Consequently, suitable measurement techniques have to be developed and validated to support ... [more ▼]

Deformation metrology of complex shape space structure and reflectors is a recurrent problem addressed by ESA. Consequently, suitable measurement techniques have to be developed and validated to support relevant on-ground qualification and verification testing. Holographic techniques in the visible wavelengths are common for measuring the surface displacement of object. However the short wavelength induces high stability criteria which are so severe that they often prevent the measurement of large space structures under good conditions. We propose to use a wavelength longer than the usual visible ones to render such holographic displacement measurement techniques less sensitive to external perturbations. For this we consider CO2 laser emitting at 10.6 μm which correspond to the long-wavelength infrared (LWIR) spectrum. The most important element for performing holography is to use an adequate recording medium. However no convincing holographic recording media exists in LWIR and we decided to investigate the possibility of electronic hologram recording, such as electronic speckle pattern interferometry (ESPI). This possibility is feasible nowadays thanks to various thermal imaging technologies such has uncooled microbolometers sensors commonly found in thermographic cameras. In this study, we analyse how it is possible to measure surface displacements of specular objects, which do not produce speckle, using speckle interferometry by the mean of a scattering diffuser. We then apply the ESPI technique at LWIR for measuring displacements of a large parabolic reflector. [less ▲]

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See detailCounterdiffusion protein crystallisation in microgravity and its observation with PromISS (Protein Microscope for the International Space Station)
Zegers, Ingrid; Carotenuto, Luigi; Evrard, Christine ULg et al

in Microgravity Science and Technology (2006), XVIII

The crystallisation by counterdiffusion is a very efficient technique for obtaining high-quality protein crystals. A prerequisite for the use of counterdiffusion techniques is that mass transport must be ... [more ▼]

The crystallisation by counterdiffusion is a very efficient technique for obtaining high-quality protein crystals. A prerequisite for the use of counterdiffusion techniques is that mass transport must be controlled by diffusion alone. Sedimentation and convection can be avoided by either working in gelled systems, working in systems of small dimensions, or in the absence of gravity. We present the results from experiments performed on the ISS using the Protein Microscope for the International Space Station (PromISS), using digital holography to visualise crystal growth processes. We extensively characterised three model proteins for these experiments (cablys3*lysozyme, triose phosphate isomerase, and parvalbumin) and used these to assess the ISS as an environment for crystallisation by counterdiffusion. The possibility to visualise growth and movement of crystals in different types of experiments (capillary counterdiffusion and batch-type) is important, as movement of crystals is clearly not negligible. [less ▲]

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See detailPattern recognition with a digital holographic microscope working in partially coherent illumination
Dubois, Frank; Minetti, Christophe; Monnom, Olivier et al

in Applied Optics (2002), 41(20), 4108-4119

We describe the implementation of the automatic spatial-frequency-selection filter for recognition of patterns obtained with a digital holographic microscope working with a partially coherent source. The ... [more ▼]

We describe the implementation of the automatic spatial-frequency-selection filter for recognition of patterns obtained with a digital holographic microscope working with a partially coherent source. The microscope provides the complex-optical-amplitude field that allows a refocusing plane-by-plane of the sample under investigation by numerical computation of the optical propagation. By inserting a correlation filter in the propagation equation, the correlation between the filter and the propagated optical field is obtained. In this way, the pattern is located in the direction of the optical axis. Owing to the very weak noise level generated by the partially coherent source, the correlation process is shift invariant. Therefore the samples can be located in the three dimensions. To have a robust recognition process, a generalized version of the automatic spatial-frequency-selection filters has been implemented. The method is experimentally demonstrated in a two-class problem for the recognition of protein crystals. (C) 2002 Optical Society of America. [less ▲]

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See detailHolographic camera with BSO applied to microgravity fluid experiment aboard ISS
Georges, Marc ULg; Joannes, Luc; Thizy, Cédric ULg et al

in Nolte, D.; Salamo, G.; Siahmakoun, A. (Eds.) et al Photorefractive Effects, Materials, and Devices (2001, July)

We present the preliminary development steps of a holographic interferometer using a BSO crystal for the monitoring of fluids experiments under microgravity conditions. This set-up could be included in ... [more ▼]

We present the preliminary development steps of a holographic interferometer using a BSO crystal for the monitoring of fluids experiments under microgravity conditions. This set-up could be included in the Fluid Science Laboratory (FSL, a module dedicated to fluid physics experiment onboard the International Space Station-ISS). Some preliminary studies have been carried out. An optimized configuration has been found allowing a fast recording (50 milliseconds) and large number of readouts (>1000) for analysis of events over a long period without reducing the measurement resolution. We present examples of Rayleigh-Benard convection quantitative measurement performed with a laboratory instrument prototype. [less ▲]

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