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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)

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See detailVérification expérimentale de modèles opto-thermo-élastiques simulés avec le logiciel OOFELIE Multiphysics
Mazzoli, Alexandra ULg; Saint-Georges, Philippe; Orban, Anne ULg et al

in 12ème colloque international francophone sur les Méthodes et Techniques Optiques pour l'Industrie (2011, November)

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See detailUsing Holography to reduce aircraft costs
Georges, Marc ULg

Article for general public (2011)

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See detailImaging polarimeters based on Liquid Crystal Variable Retarders: an emergent technology for space instrumentation
Alvarez-Herrero, A.; Uribe-Patarroyo, N.; Garcia Parejo, P. et al

in Show, J. A.; Scott Tyo, J. (Eds.) Proc. SPIE Vol 8160 on Polarization Science and Remote Sensing V (2011, September 09)

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See detailSpace-qualified liquid-crystal variable retarders for wide-field-of-view coronographs
Uribe-Patarroyo, N.; Alvarez-Herrero, A.; Garcia Parejo, P. et al

in Fineschi, Silvano; Fennelly, Judy (Eds.) Proc. SPIE Vol 8148 on Solar Physics and Space Weather Instrumentation IV (2011, August)

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See detailLIBS : Identification rapide de composants chimiques. Application au recyclage des matériaux et détection de pollution du sol
Georges, Marc ULg

Conference (2011, May 13)

La technique LIBS (Laser Induced Breakdown Spectroscopy) permet une analyse rapide in situ des éléments chimiques sans préparation de l'échantillon. La LIBS consiste à illuminer un échantillon à analyser ... [more ▼]

La technique LIBS (Laser Induced Breakdown Spectroscopy) permet une analyse rapide in situ des éléments chimiques sans préparation de l'échantillon. La LIBS consiste à illuminer un échantillon à analyser avec une impulsion laser nanoseconde et concentrée par un système optique. Il en résulte la production en surface du matériau d'un plasma qui émet de la lumière dont le contenu spectral est ensuite analysé à distance. La LIBS a diverses applications dans le secteur de l'environnement. Dans la présentation, nous mettons en avant les applications dans la recherche de polluants ainsi que la possibilité de trier les vitrocéramiques dans les déchets verriers. Cette dernière application a été mise au point par le Centre Spatial de Liège avec le support financier de FOST Plus. [less ▲]

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See detailMesures LASER
Georges, Marc ULg

Learning material (2011)

Nous passons en revue les différentes méthodes de mesures laser, par champ complet ou ponctuelles, que ce soit pour la mesure de déformation, les mesures de distance, vitesse, épaisseur, ou les mesures ... [more ▼]

Nous passons en revue les différentes méthodes de mesures laser, par champ complet ou ponctuelles, que ce soit pour la mesure de déformation, les mesures de distance, vitesse, épaisseur, ou les mesures dans les fluides, les gaz ainsi que des techniques particulières comme la LIBS utilisées en analyse chimique [less ▲]

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See detailFANTOM FP7 Project : Innovative NDT Technique Development. Single sensor for simultaneous temporal and spatial full-field thermography and deformation measurements in structural tests
Georges, Marc ULg

Conference given outside the academic context (2011)

The European FP7 FANTOM project aims at developing an innovative Non Destructive Testing technique based on simultaneous acquisition of thermal and deformation fields by a single sensor. The technique is ... [more ▼]

The European FP7 FANTOM project aims at developing an innovative Non Destructive Testing technique based on simultaneous acquisition of thermal and deformation fields by a single sensor. The technique is based on speckle interferometry with infrared laser emitting in the thermal infrared range. The applications envisaged are mainly targeted to structural testing and in particular thermo-mechanical assessment of structures under loads. Also the ability of the technique for the detection of defects will be assessed. At present the technique is demonstrated and a prototype is under construction for industrial validation in structural test facilities of Airbus. [less ▲]

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See detailFANTOM Project Overview
Georges, Marc ULg

Conference (2011, March 31)

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See detailExperimental validation of opto-thermo-elastic modeling in OOFELIE Multiphysics
Mazzoli, Alexandra ULg; Saint-Georges, Philippe; Orban, Anne ULg et al

in SPIE, Optical Systems Design (Marseille 5-8 septembre 2011) (2011)

The objective of this work is to demonstrate the correlation between a simple laboratory test bench case and the predictions of the Oofelie MultiPhysics software in order to deduce modelling guidelines ... [more ▼]

The objective of this work is to demonstrate the correlation between a simple laboratory test bench case and the predictions of the Oofelie MultiPhysics software in order to deduce modelling guidelines and improvements. For that purpose two optical systems have been analysed. The first one is a spherical lens fixed in an aluminium barrel, which is the simplest structure found in an optomechanical system. In this study, material characteristics are assumed to be well known: BK7 and aluminium have been retained. Temperature variations between 0 and +60°C from ambient have been applied to the samples. The second system is a YAG laser bar heated by means of a dedicated oven. For the two test benches thermo-elastic distortions have been measured using a Fizeau interferometer. This sensor measures wavefront error in the range of 20 nm to 1 μm without physical contact with the optomechanical system. For the YAG bar birefringence and polarization measurements have also been performed using a polarimetric bench. The tests results have been compared to the predictions obtained by Oofelie MultiPhysics which is a multiphysics toolkit treating coupled problems of optics, mechanics, thermal physics, electricity, electromagnetism, acoustics and hydrodynamics. From this comparison modelling guidelines have been issued with the aim of improving the accuracy of computed thermo-elastic distortions and their impact on the optical performances. [less ▲]

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See detailInterférométrie holographique et de speckle en infrarouge thermique : développements actuels, applications et perspectives
Georges, Marc ULg

in Smigielski, P. (Ed.) Actes du Onzième colloque francophone Méthodes et Techniques Optiques pour l'Industrie (2010, November)

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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)

Detailed reference viewed: 49 (10 ULg)