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 (2016), 8

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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 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 ▲]

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

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

Thermography and different variants of holography (holographic interferometry, speckle interferometry, shearography) are full-field non-contact techniques which are used in nondestructive testing ... [more ▼]

Thermography and different variants of holography (holographic interferometry, speckle interferometry, shearography) are full-field non-contact techniques which are used in nondestructive testing applications. In particular they are attractive for damage detection in composite materials compared to other methods measuring in one point and which require scanning and contact with the samples, like ultrasounds. Currently thermography is a step forward compared to holographic techniques for this application. Indeed it is easier to interpret. Many thermography configurations and variants exist, from exciting sources to post-processing. Such a variety exists also among the holographic techniques but to a less extent. We will see how these techniques can share some aspects and what distinguish them. Also the complementarity of both will be addressed and how to combine them. At last we will discuss how processing developed for thermography can benefit to holography and vice-versa, specifically in the domain of composite materials. [less ▲]

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See detailTime-averaged phase-stepped ESPI with CO2 laser and shearography in the visible for identification of vibration mode shapes
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Georges, Marc ULg

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

We present investigation of interferometric methods for vibration mode identification to be applied on shakers in industrial environment. We consider long wave infrared ESPI in time-averaged mode with the ... [more ▼]

We present investigation of interferometric methods for vibration mode identification to be applied on shakers in industrial environment. We consider long wave infrared ESPI in time-averaged mode with the use of phase-stepping which allows transforming Bessel fringes, typical to the time averaging, into phase values which provide a better way for identification of vibration mode shapes. The use of long laser wavelength allows measuring larger amplitudes of vibrations compared to what is achieved in visible light. Also longer wavelengths allow lower sensitivity to external perturbations. Time-averaged phase-stepped shearography in visible is also used as a compared alternative to LWIR ESPI for working in industrial environments. Although not demonstrated here, an interesting feature for the future investigations on LWIR ESPI is its potentiality of simultaneous temperature measurement during vibrations [less ▲]

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See detailUse of specklegrams background terms for speckle photography combined with phase-shifting electronic speckle pattern interferometry
Zemmamouche, Redouane; Vandenrijt, Jean-François ULg; Medjahed, Aïcha et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2015), 54(8), 084110

Electronic speckle pattern interferometry (ESPI) is combined with digital speckle photography (DSP) to measure out-of-plane deformation in the presence of large in-plane translation or rotation. ESPI is ... [more ▼]

Electronic speckle pattern interferometry (ESPI) is combined with digital speckle photography (DSP) to measure out-of-plane deformation in the presence of large in-plane translation or rotation. ESPI is used to measure out-of-plane displacements smaller than the speckle diameter. In-plane displacements larger than the speckle size are obtained by DSP using artifacts images computed from the phase-stepped specklegrams. Previous works use the specklegram modulation for that purpose, but we show that this can lead to errors in the case of low modulation. In order to avoid this, a simple averaging of phase-stepped specklegrams allows obtaining the average irradiance, which contains information on the speckled object image. The latter can be used more efficiently than the modulation in DSP and is simpler to compute. We also perform a numerical simulation of specklegrams, which show that the use of background terms is much more stable against some error sources as compared to modulation. We show experimental evidence of this in various experiments combining out-of-plane ESPI measurements with in-plane translations or rotations obtained by our DSP method. The latter has been used efficiently to restore phase loss in out-of-plane ESPI measurements due to large in-plane displacements. [less ▲]

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See detailDevelopment of a full fiber-coupled laser ultrasound robotic system using two-wave mixing 1064 nm detection and 532 nm YAG generation
Vandenrijt, Jean-François ULg; Simar, Juan Felipe ULg; Thizy, Cédric ULg et al

in Laser Ultrasonics and Advanced Sensing (2015, June)

An all-fibered laser ultrasonic system for complex shape composite parts is presented. It is based on two-wave mixing detection and a long pulse laser working at 1064 nm and generation by a fibered YAG Q ... [more ▼]

An all-fibered laser ultrasonic system for complex shape composite parts is presented. It is based on two-wave mixing detection and a long pulse laser working at 1064 nm and generation by a fibered YAG Q-switch laser working at 532 nm. A compact optical head combining both beams is interfaced to a robot system for scanning. Some practical issues of this system are studied. [less ▲]

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See detailSpeckle interferometry in the long-wave infrared for combining holography and thermography in a single sensor. Applications to nondestructive testing: the FANTOM project
Georges, Marc ULg

in Lehmann, Peter; Osten, Wolfgang; Albertazzi, Armando (Eds.) Optical Measurement Systems for Industrial Inspection IX (2015, June)

Speckle interferometry in the thermal wavelengths range (long-wave infrared, 8-14 μm), combining a CO2 laser and recording with an uncooled microbolometer camera is presented. In this wavelength range ... [more ▼]

Speckle interferometry in the thermal wavelengths range (long-wave infrared, 8-14 μm), combining a CO2 laser and recording with an uncooled microbolometer camera is presented. In this wavelength range specklegrams are affected by the thermal radiation emitted by objects at room temperature. This allows simultaneously capturing temperature and surface shape information about objects. The FANTOM project is based on this concept and an instrument was developed to take advantage of this natural data fusion. It has been used in a variety of nondestructive testing applications where both information are useful, specifically in aeronautical composite structures. [less ▲]

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See detailLong-wave infrared digital holographic interferometry for deformation measurement of the segmented detector array of the space EUCLID mission
Vandenrijt, Jean-François ULg; Thizy, Cédric ULg; Beaumont, Florent et al

in Digital Holography and Three-Dimensional Imaging (2015, May)

Digital holographic interferometry in LWIR is used for following the deformation and relative movement of an assembly of detectors to be used in space. The setup is incorporated in a vacuum chamber for ... [more ▼]

Digital holographic interferometry in LWIR is used for following the deformation and relative movement of an assembly of detectors to be used in space. The setup is incorporated in a vacuum chamber for cryogenic testing. [less ▲]

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See detailLong-wave infrared digital holography
Georges, Marc ULg

in Picart, Pascal (Ed.) New Techniques in Digital Holography (2015)

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See detailFeature issue of digital holography and 3D imaging (DH): introduction
Hayasaki, Yoshio; Liu, Jung-Ping; Georges, Marc ULg

in Applied Optics (2015), 54(1), 1-2

The OSA Topical Meeting “Digital Holography and 3D Imaging (DH)” was held in Seattle, Washington, 13–17 July 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO ... [more ▼]

The OSA Topical Meeting “Digital Holography and 3D Imaging (DH)” was held in Seattle, Washington, 13–17 July 2014. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. In this year (2014), Optics Express (OE) and AO jointly decided to have one such feature issue in each journal. The feature issue includes 27 papers and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The DH meeting will continue in the future, as expected, and the next meeting is scheduled to be held on24–28 May 2015, at Shanghai Institute of Optics and Fine Mechanics, Shanghai, China. [less ▲]

Detailed reference viewed: 56 (5 ULg)