References of "Georges, Marc"
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See detailPerformances of Volume Phase Holographic grating for space applications: study of the radiation effect
Loicq, Jerôme ULg; Georges, Marc ULg; Stockman, Yvan ULg et al

in Applied Optics (2013), 52(34),

The special properties of volume phase holographic gratings make them promising candidates for spectrometry applications where high spectral resolution, low levels of straylight, and low polarization ... [more ▼]

The special properties of volume phase holographic gratings make them promising candidates for spectrometry applications where high spectral resolution, low levels of straylight, and low polarization sensitivity are required. Therefore it is of interest to assess the maturity and suitability of volume phase holographic gratings as enabling technologies for future space missions, with demanding requirements for spectrometry. One of the main areas of research is related to grating ageing under space radiation. In the present paper, two volume grating technologies are analyzed and compared under gamma irradiation. The performances of both technologies, the photo–thermo–refractive glass and the Dichromated Gelatin, are tested on samples and assessed in the and near-infrared bands. The diffraction efficiency degradation under gamma irradiation is assessed. [less ▲]

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See detailComparaison de techniques CND émergentes sur des pièces aéronautiques en matériaux composites
Georges, Marc ULg; Thizy, Cédric ULg; Lewandowski, Jacques et al

Conference (2013, November)

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See detailComparison of 3 emerging optical NDI techniques on complex shaped composite structures based on carbon fiber
Georges, Marc ULg

Conference (2013, October 01)

Thermography, shearography and laser ultrasonics are 3 contactless emerging techniques which allow nondestructive inspection of composite structures. Thermography and shearography are full-field ... [more ▼]

Thermography, shearography and laser ultrasonics are 3 contactless emerging techniques which allow nondestructive inspection of composite structures. Thermography and shearography are full-field techniques yielding measurement of respectively local temperature variations or deformations of a structure undergoing a stress (thermal, pressure, vibration). Laser ultrasonics allows remote ultrasound generation in the composite by thermoelastic effect followed by remote measurement of the surface displacements under the effect of the ultrasound echoes without coupling. This point-like technique requires scanning. The three techniques have been selected in our project since they allow inspection of complex shaped parts. We present compared results obtained on a variety of aeronautical industrial composite parts. [less ▲]

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See detailMobile speckle interferometer in the long-wave infrared for aeronautical nondestructive testing in field conditions
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Alexeenko, Igor et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2013), 52(10),

Abstract We present the development of a speckle interferometer based on CO2 laser and using a thermal infrared camera based on uncooled microbolometer array. It is intended to be used for monitoring ... [more ▼]

Abstract We present the development of a speckle interferometer based on CO2 laser and using a thermal infrared camera based on uncooled microbolometer array. It is intended to be used for monitoring deformations as well as flaw detection in aeronautical composites, with a smaller sensitivity to displacement compared to equivalent system using visible lasers. Moreover the long wavelength allows working with such interferometer under out-of-laboratory conditions. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications under field working conditions. [less ▲]

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See detailComparison of three NDT techniques for the inspection of aeronautic composite structures
Dubé, Robin; Scheed, Laurent; Lewandoswki, Jacques et al

Conference (2013, July 28)

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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

in Digital Holography and Three-Dimensional Imaging, OSA Technical Digest (online) (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 detailHolographic interferometry based on photorefractive crystal to measure 3D thermo-elastic distortion of composite structures and comparison with finite element models
Thizy, Cédric ULg; Eliot, F.; Olympio, K.R. et al

in Lehmann, Peter (Ed.) Proc. SPIE Vol 8788 on Optical Measurement Systems for Industrial Inspection VIII (2013, May)

Thermo-elastic distortions of composite structures have been measured by a holographic camera using a BSO photorefractive crystal as the recording medium. The first test campaign (Phase 1) was performed ... [more ▼]

Thermo-elastic distortions of composite structures have been measured by a holographic camera using a BSO photorefractive crystal as the recording medium. The first test campaign (Phase 1) was performed on CFRP struts with titanium end-fittings glued to the tips of the strut. The samples were placed in a vacuum chamber. The holographic camera was located outside the chamber and configured with two illuminations to measure the relative out-of-plane and in-plane (in one direction) displacements. The second test campaign (Phase 2) was performed on a structure composed of a large Silicon Carbide base plate supported by 3 GFRP struts with glued Titanium end-fittings. Thermo-elastic distortions have been measured with the same holographic camera used in phase 1, but four illuminations, instead of two, have been used to provide the three components of displacement. This technique was specially developed and validated during the phase 2 in CSL laboratory. The system has been designed to measure an object size of typically 250x250 mm²; the measurement range is such that the sum of the largest relative displacements in the three measurement directions is maximum 20 μm. The validation of the four-illuminations technique led to measurement uncertainties of 120 nm for the relative in-plane and out-of-plane displacements, 230 nm for the absolute in-plane displacement and 400 nm for the absolute out-of-plane displacement. For both campaigns, the test results have been compared to the predictions obtained by finite element analyses and the correlation of these results was good [less ▲]

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See detailEvaluation de technologies émergentes pour le contrôle non destructif de composites aéronautiques
Georges, Marc ULg; Lewandowski, Jacques

Scientific conference (2013, March 13)

La proportion des pièces en composite utilisées dans les structures des aéronefs ne cesse de croître, posant de nouveaux défis techniques et économiques aux méthodes de contrôle non destructif (CND ... [more ▼]

La proportion des pièces en composite utilisées dans les structures des aéronefs ne cesse de croître, posant de nouveaux défis techniques et économiques aux méthodes de contrôle non destructif (CND) classiquement utilisées: géométries complexes, larges surfaces à inspecter, impossibilité d’immerger certains composants. La thermographie infrarouge, la shearographie et le laser-ultrasons sont des techniques émergentes encore assez peu répandues dans l’industrie, mais qui présentent un fort potentiel vis-à-vis de ces nouvelles problématiques. Cet atelier présentera ces trois techniques en s’appuyant sur des résultats d’inspection sur des pièces aéronautiques variées: bord d’attaque, raidisseur en Omega, secteur de virole, plancher complexe avec raidisseurs. Ces résultats sont le fruit d’une collaboration entre le Centre spatial de Liège (Belgique), le Centro de Tecnologias Aeronauticas (Espagne) et le Centre technologique en aérospatiale (Canada). [less ▲]

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See detailTests non-destructifs (NDT) pour structures en matériaux composites
Georges, Marc ULg

Scientific conference (2013, February 28)

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See detailNondestructive testing by using long wave infrared interferometric techniques with CO2 lasers and microbolometer arrays
Alexeenko, Igor; Vandenrijt, Jean-François ULg; Pedrini, Giancarlo et al

in Applied Optics (2013), 52(1), 57-67

We describe three different interferometric techniques (electronic speckle pattern interferometry, digital holographic interferometry, digital shearography), using a long wave infrared radiation produced ... [more ▼]

We describe three different interferometric techniques (electronic speckle pattern interferometry, digital holographic interferometry, digital shearography), using a long wave infrared radiation produced by a CO2 laser and recording on a microbolometers array. Experimental results showing how these methods can be used for nondestructive testing are presented. Advantages and disadvantages of these approaches are discussed. [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 detailLong-wave infrared digital holography for the qualification of large space reflectors
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Georges, Marc ULg et al

Conference (2012, October 09)

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 ... [more ▼]

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. [less ▲]

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See detailUV radiation effects on liquid crystal variable retarders for aerospace applications
Garcia Parejo, Pilar; Alvarez-Herrero, Alberto; Uribe-Patarroyo, Nestor et al

Conference (2012, August)

Liquid-Crystal Variable Retarders (LCVRs)1 are optical devices that provide a variable optical retardance accomplished by the application of electric fields. Traditionally, they have been used as light ... [more ▼]

Liquid-Crystal Variable Retarders (LCVRs)1 are optical devices that provide a variable optical retardance accomplished by the application of electric fields. Traditionally, they have been used as light polarization modulators for polarimetric applications in ground telescopes2, and more recently they took part in the polarisation modulation package of the Imaging Magnetograph eXperiment (IMaX)3, where the LCVRs were launched successfully on-board the Sunrise mission, a stratospheric balloon that was flown from Antarctica to study the solar magnetic fields. This mission was the precursor of the Solar Orbiter mission of the European Space Agency (ESA), where the liquid crystals will be used as polarisation modulators onboard a space mission for the first time in two instruments: the Polarimetric and Helioseismic Imager (SO/PHI) and the Multi-Element Telescope for Imaging and Spectroscopy (METIS). Any on-board element used for aerospace applications must be able to survive the harsh environmental space conditions including UV radiation, gamma radiation, vibrational tests, thermal-vacuum... In this sense, LCVRs have been recently validated to be used under the space conditions of the Solar Orbiter mission, in the framework of the ESA project: “Validation of LCVRs for the Solar Orbiter Polarisation Modulation Package”. In this project, a set of LCVRs with different design parameters has been analyzed under the different space environmental conditions. These design parameters include the architecture of the LCVR cell, using Anti-Parallel Aligned Nematic (APAN) and Hybrid Aligned Nematic (HAN) architectures, the type of liquid crystal molecules, using different commercial nematic liquid crystal mixtures with high and low birefringence and positive and negative dielectric anisotropy, different homogeneous and homeotropic polyimide alignment layers and different glass plates. Among the space environmental components, the UV radiation needs special consideration due to the organic nature of the liquid crystal molecules and the alignment layers that consisted of rubbed polyimide layers. In this work, we present the main results of the UV radiation test campaign carried out in the LCVRs consisting of the performance of a thorough optical characterization of the LCVRs, including optical retardance and response times measurements at different voltages performed by the ellipsometry technique, and optical transmission measurements, before and after irradiating the LCVRs with UV light at different doses, in two different spectral ranges: 200 -400 nm and 160-200 nm. The main degradation effects observed in the LCVRs was a progressive reduction of the retardance range of the LCVRs which points out a decrease of the birefringence of the liquid crystal molecules or the increase of the pretilt angle due to the degradation of the polyimide layers, and an increase of the response times of the cells. Nevertheless, the changes observed do not involve the destruction of the LCVRs and they keep fulfilling the requirements for the Solar Orbiter mission becoming in a promising technology for aerospace applications. [less ▲]

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See detailInvestigation on the High Efficiency Volume Bragg gratings performances for spectrometry in space environment: Preliminary results
Loicq, Jerôme ULg; Georges, Marc ULg; Gaspar Venancio, Luis Miguel

in Telescope and systems (2012, July)

The special properties of Volume Bragg Gratings (VBGs) make them good candidates for spectrometry applications where high spectral resolution, low level of straylight and low polarisation sensitivity are ... [more ▼]

The special properties of Volume Bragg Gratings (VBGs) make them good candidates for spectrometry applications where high spectral resolution, low level of straylight and low polarisation sensitivity are required. Therefore it is of interest to assess the maturity and suitability of VBGs as enabling technology for future ESA missions with demanding requirements for spectrometry. The VBGs suitability for space application is being investigated in the frame of a project led by CSL and funded by the European Space Agency. The goal of this work is twofold: first the theoretical advantages and drawbacks of VBGs with respect to other technologies with identical functionalities are assessed, and second the performances of VBG samples in a representative space environment are experimentally evaluated. The performances of samples of two VBGs technologies, the Photo-Thermo-Refractive (PTR) glass and the DiChromated Gelatine (DCG), are assessed and compared in the H, O2-B and NIR bands. The tests are performed under vacuum condition combined with temperature cycling in the range of 200 K to 300K. A dedicated test bench experiment is designed to evaluate the impact of temperature on the spectral efficiency and to determine the optical wavefront error of the diffracted beam. Furthermore the diffraction efficiency degradation under gamma irradiation is assessed. Finally the straylight, the diffraction efficiency under conical incidence and the polarisation sensitivity is evaluated. [less ▲]

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See detailSpeckle interferometry at 10 µm with CO2 lasers and microbolometers array
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

in Kieffer, Jean-Claude (Ed.) Photonics North 2012 (2012, June 06)

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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)

Detailed reference viewed: 27 (5 ULg)