References of "Georges, Marc"
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See detailLaser optics in space failure risk due to laser induced contamination
Kokkinos, Dimitrios ULg; Schroeder, Helmut; Fleury-Frenette, Karl ULg et al

in CEAS Space Journal (2017), 8

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See detailDigital holographic interferometry in the long-wave infrared and temporal phase unwrapping for measuring large deformations and rigid body motions of segmented space detector in cryogenic test (invited paper)
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Martin, Laurent et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2016), 55(12), 121723

We present digital holographic interferometry in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array (FPA) to be used in a space mission. The ... [more ▼]

We present digital holographic interferometry in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array (FPA) to be used in a space mission. The long wavelength was chosen for its ability to allow measurement of displacements 20 times larger than DHI in the visible and which were foreseen with the test object under large temperature variations. The latter is a mosaic of 4×4 detectors assembled on a frame. DHI was required to assess the global deformation of the assembly, the deformation of each detector, and piston movements of each of them with respect to their neighbors. For that reason we incorporated the temporal phase unwrapping by capturing a sufficiently high number of holograms between which the phase does not undergo large variations. At last, since the specimen exhibits specular reflectivity at that wavelength, it is illuminated by means of a reflective diffuser. [less ▲]

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See detailSpeckle Metrology
Mendoza Santoyo, Fernando; Georges, Marc ULg; Lehmann, Peter et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2016), 55(12), 121701

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See detailNon-contact emerging nondestructive techniques for aerospace composite inspection
Georges, Marc ULg

Scientific conference (2016, November 17)

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See detailL'optique spatiale en Wallonie: de la génèse aux développements récents
Georges, Marc ULg; Denis, Stefan; Joannes, Luc

Scientific conference (2016, November 10)

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See detailHolographie numérique en infrarouge lointain - Applications aérospatiales
Georges, Marc ULg; Vandenrijt, Jean-François ULg; Languy, Fabian ULg et al

Conference (2016, November)

L'holographie numérique en infrarouge lointain, utilisant un laser CO2 émettant vers 10 µm et des caméras thermiques à microbolomètres, permet la mesure de grandes déformations et de s'affranchir des ... [more ▼]

L'holographie numérique en infrarouge lointain, utilisant un laser CO2 émettant vers 10 µm et des caméras thermiques à microbolomètres, permet la mesure de grandes déformations et de s'affranchir des perturbations environnementales plus facilement qu'en lumière visible. Nous l'appliquons dans le cas de structures spatiales subissant des cyclages thermiques en régime cryogénique sous vide, ce qui induit des déplacements de grande ampleur. Nous passerons en revue les différentes expériences effectuées au Centre Spatial de Liège et discuterons des recherches en cours, notamment pour utiliser des longueurs d'onde plus grande (ondes Terahertz) [less ▲]

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See detailLaser Ultrasound for NDT: investigation of the generation beam shape
Languy, Fabian ULg; Perrard, Aurélie; Vandenrijt, Jean-François ULg et al

Poster (2016, July)

Usually laser ultrasonic systems use an infrared laser operating at 10 µm to generate the ultrasound in CFRP objects. However this system suffer from an important drawback: optical fiber cannot be used to ... [more ▼]

Usually laser ultrasonic systems use an infrared laser operating at 10 µm to generate the ultrasound in CFRP objects. However this system suffer from an important drawback: optical fiber cannot be used to transport the high energy beam from the laser output to the target which limits the flexibility of the system to investigated complex shaped objects. To overcome this issue, visible light can be used to generate ultrasound. In our case we use a fiber-coupled laser operating at 532 nm. The output end of the optical fiber is placed on an industrial robot arm. The investigated object remains stationary while the optical fiber mounted on the robot arm scan the object. This system offers large flexibility but laser generation at 532 nm is known to be less efficient than CO 2 system emitting at 10 µm. Increasing the visible pulse power is one of the options but optics and CRFF object will be damaged before the same echo level as CO2 generation can be obtained. An alternative solution consists in the investigation of the generation beam size and shape. We recently developed an optical design composed of an axicon lens able to generate annular beam. The diameter of the beam can be adapted. If the axicon lens is removed the optical system provides a disk whose diameter can also be adapted onto the investigated object. Ray-traycing simulations performed with ASAP and experimental beam profile investigated with a beam profiler show good agreement between theoretical and experimental optical design. An experimental comparison between ring and disk shapes will be presented. The comparisons take into account the beam diameter and the beam intensity but also the effect of the angle of incidence will be presented. [less ▲]

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See detailPerformances comparison of a laser ultrasonic system using 10.6 µm infrared or 532 nm visible generation beam for the investigation of CFRP
Vandenrijt, Jean-François ULg; Walter, Julien; Brouillette, Tomy et al

Conference (2016, July)

The investigation of complex shaped carbon fiber parts is a common need of the industry. Classical ultrasonic systems are commonly used, wide-spread and very efficient. However, these techniques are often ... [more ▼]

The investigation of complex shaped carbon fiber parts is a common need of the industry. Classical ultrasonic systems are commonly used, wide-spread and very efficient. However, these techniques are often limited to simple shape objects. Major problems arise when the shape of the element to be investigated is complex (peak, valley, small radius of curvature…). To overcome these problems laser ultrasonic systems can be used and the recent developments show promising results. Laser ultrasonic systems can use different wavelengths for ultrasound generation. Usually CO2 lasers emitting at 10.6 µm wavelength are used. When a laser ultrasonic system is mounted on a robotic arm, very complex shaped objects can be considered. However, the optical fibers for 10.6 µm wavelength are not capable to cope with laser ultrasonic system requirements. Therefore, infrared systems use jointed articulated beam delivery systems which reduce the flexibility of the robot arm and significantly limit the feasible scan paths. To circumvent this limitation, an all-fibered laser ultrasonic system can be used. In our case the ultrasound is generated with a pulsed laser operating at 532 nm. This system is placed on a robotic arm, the beam delivery is performed through an optical fiber only. Therefore, this system is capable of analyzing very complex shaped objects due to the use of optical fiber only for laser beam transport. But visible generation is known to be less efficient and produces lower quality signals. In order to balance the advantages and limitations of both of these systems a CFRP plate including artificial defects has been investigated with different ultrasonic systems. First we used classical phased-array ultrasounds as a reference to compare the performances of visible and infrared generation systems. The plate has then been investigated with a 10.6 µm laser ultrasonic system. The results are compared with an all-fibered laser ultrasonic system working at 532 mn wavelength. Data acquired by each system allow comparing the visibility of the ultrasonic echoes and the amplitude of background noise. We observe the impact of frequency filtering. We show the main differences on the A-scans and C-scan generated by each system. From these elements, we show the advantages and limitations of each system for the investigation of CFRP with a focus on complex shaped object. [less ▲]

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See detailVibration mode shapes visualization in industrial environment by real-time time-averaged phase-stepped electronic speckle pattern interferometry at 10.6  μm and shearography at 532 nm
Languy, Fabian ULg; Vandenrijt, Jean-François ULg; Thizy, Cédric ULg et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2016), 55(12), 121704

We present our investigations on two interferometric methods suitable for industrial conditions dedicated to the visualization of vibration modes of aeronautic blades. First, we consider long-wave ... [more ▼]

We present our investigations on two interferometric methods suitable for industrial conditions dedicated to the visualization of vibration modes of aeronautic blades. First, we consider long-wave infrared (LWIR) electronic speckle pattern interferometry (ESPI). The use of long wavelength allows measuring larger amplitudes of vibrations compared with what can be achieved with visible light. Also longer wavelengths allow lower sensitivity to external perturbations. Second, shearography at 532 nm is used as an alternative to LWIR ESPI. Both methods are used in time-averaged mode with the use of phase-stepping. This allows transforming Bessel fringes, typical to time averaging, into phase values that provide higher contrast and improve the visualization of vibration mode shapes. Laboratory experimental results with both techniques allowed comparison of techniques, leading to selection of shearography. Finally a vibration test on electrodynamic shaker is performed in an industrial environment and mode shapes are obtained with good quality by shearography. [less ▲]

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See detailThermography vs holographic techniques for nondestructive testing of composites: similarities, differences and potential cross-fertilization
Georges, Marc ULg

Conference (2016, May)

Thermography and holography are full-field non-contact techniques which are used in nondestructive testing (NDT) applications. Thermography is a step forward to holography for damage detection because it ... [more ▼]

Thermography and holography are full-field non-contact techniques which are used in nondestructive testing (NDT) applications. Thermography is a step forward to holography for damage detection because it is easier to interpret. We discuss their common aspects and what distinguish them. Also the complementarity of both is addressed and an innovative combination of both is proposed. At last we show how processing developed for thermography can benefit to holography, specifically in the domain of composite materials [less ▲]

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See detailPhotoconductivity and photoconversion at a photorefractive thin crystal plate
Frejlich, Jaime; de Oliveira, Ivan; de Araujo, William R. et al

in Optical Materials (2016), 55

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See detailPhotorefractives for holographic interferometry and nondestructive testing
Georges, Marc ULg

in Blanche, Pierre-Alexandre (Ed.) Photorefractive Organic Materials and Applications (2016)

Thanks to its high sensitivity to displacement, holography is very well suited for metrology. In the case of holographic interferometry (HI), interference occurs between the object wavefront and a ... [more ▼]

Thanks to its high sensitivity to displacement, holography is very well suited for metrology. In the case of holographic interferometry (HI), interference occurs between the object wavefront and a wavefront reconstructed by a hologram allowing a comparison between different objects, or different states of the same object. This chapter first discusses the importance of HI compared to other techniques such as electronic or computer based interferometry, then the author is developing various methodologies for holographic metrology, including real time, double exposure, and time averaged HI. Material considerations are covered and the specific case of photorefractive polymer and crystals are analyzed. Several experiments of nondestructive testing on industrial systems are discussed with measurement configurations relevant for thermal analysis, vibration, defect detection, and even historic artifact investigation. [less ▲]

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See detailReal-time measurement of temperature variation during nanosecond pulsed laser induced contamination deposition
Kokkinos, Dimitrios ULg; Gailly, Patrick ULg; Georges, Marc ULg et al

in Applied Optics (2015), 54(36), 10579

In this paper a study of the heat generation during UV Laser Induced Contamination (LIC) and potentially resulting subsequent thermal damage is presented. This becomes increasingly interesting when optics ... [more ▼]

In this paper a study of the heat generation during UV Laser Induced Contamination (LIC) and potentially resulting subsequent thermal damage is presented. This becomes increasingly interesting when optics with delicate coatings are involved. During LIC radiation can interact with outgassing molecules both in the gas phase and at the surface, triggering chemical and photo-fixation reactions. This is a major hazard, in particular for laser units operating under vacuum conditions such as for space applications. The intense photon flux not only affects the contaminant deposition rate but also alters their chemical structure that can increase their absorption coefficient. Over cumulative irradiation shots these molecules formed deposits that increasingly absorb photons and produce heat as a by-product of de-excitation eventually leading to thermal damage. One could better asses the risk of the latter with the knowledge of temperature during the contamination process. For this purpose thermoreflectance technique is used here to estimate the temperature variation from pulse to pulse during contamination deposition through the analysis of a temperature-dependent surface reflectance signal. [less ▲]

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See detailComparison of active thermography techniques for the inspection and defect characterisation of carbon fiber composites
Fernandes, Henrique; Georges, Marc ULg; Crabus, Georges et al

Conference (2015, December)

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See detailPhotorefractive holographic camera for monitoring deformations of MEMS
Georges, Marc ULg; Thizy, Cédric ULg

in Journal of Micro/Nanolithography, MEMS, and MOEMS (2015), 14(4), 041301

We present the development of a holographic interferometer based on dynamic hologram recording with photorefractive crystals of the sillenite family and which is adapted for the observation of MEMS. A ... [more ▼]

We present the development of a holographic interferometer based on dynamic hologram recording with photorefractive crystals of the sillenite family and which is adapted for the observation of MEMS. A compact portable system was already presented in the past and used in various metrology and nondestructive applications on large scattering objects. It was emphasized the great versatility of the instrument which allows high resolution measurements. Here we show the development and achievement of an optical module which can be easily interfaced on the basic instrument, allowing small specular objects observation. Results of deformation of electrically actuated MEMS are shown. [less ▲]

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See detailCombination of temporal phase unwrapping and long-wave infrared digital holographic interferometry for metrology of mosaic detector under space simulated conditions
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Beaumont, Florent et al

in Mendoza Santoyo, Fernando (Ed.) SPECKLE 2015: VI International Conference on Speckle Metrology (2015, August)

We present digital holographic interferometry (DHI) in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array to be used in a space mission. The ... [more ▼]

We present digital holographic interferometry (DHI) in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array to be used in a space mission. The long wavelength was chosen for its ability to allow measurement of displacements 20 times larger than DHI in the visible and which were foreseen with the test object under such temperature changes. The specimen consists of 4x4 mosaic of detectors assembled on a frame. It was required to assess the global deformation of the ensemble, the deformation of each detector, and piston movements of each of them with respect to their neighbors. For that reason we incorporated the temporal phase unwrapping by capturing a sufficiently high number of holograms between which the phase does not suffer strong variations. At last since the specimen exhibit specular reflectivity at that wavelength, it is illuminated through a reflective diffuser [less ▲]

Detailed reference viewed: 40 (11 ULg)