References of "Piron, Pierre"
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See detailThe VORTEX project: first results and perspectives
Absil, Olivier ULg; Mawet, Dimitri; Delacroix, Christian ULg et al

in Marchetti, Enrico; Close, Laird; Véran, Jean-Pierre (Eds.) Adaptive Optics Systems IV (in press)

Vortex coronagraphs are among the most promising solutions to perform high contrast imaging at small angular separations from bright stars. They feature a very small inner working angle (down to the ... [more ▼]

Vortex coronagraphs are among the most promising solutions to perform high contrast imaging at small angular separations from bright stars. They feature a very small inner working angle (down to the diffraction limit of the telescope), a clear 360 degree discovery space, have demonstrated very high contrast capabilities, are easy to implement on high-contrast imaging instruments, and have already been extensively tested on the sky. Since 2005, we have been designing, developing and testing an implementation of the charge-2 vector vortex phase mask based on concentric sub-wavelength gratings, referred to as the Annular Groove Phase Mask (AGPM). Science-grade mid-infrared AGPMs were produced in 2012 for the first time, using plasma etching on synthetic diamond substrates. They have been validated on a coronagraphic test bench, showing broadband peak rejection up to 500:1 in the L band, which translates into a raw contrast of about 6e-5 at 2λ/D. Three of them have now been installed on world-leading diffraction-limited infrared cameras, namely VLT/NACO, VLT/VISIR and LBT/LMIRCam. During the science verification observations with our L-band AGPM on NACO, we observed the beta Pictoris system and obtained unprecedented sensitivity limits to planetary companions down to the diffraction limit (0.1"). More recently, we obtained new images of the HR 8799 system at L band during the AGPM first light on LMIRCam. After reviewing these first results obtained with mid-infrared AGPMs, we will discuss the short- and mid-term goals of the on-going VORTEX project, which aims to improve the performance of our vortex phase masks for future applications on second-generation high-contrast imager and on future extremely large telescopes (ELTs). In particular, we will briefly describe our current efforts to improve the manufacturing of mid-infrared AGPMs, to push their operation to shorter wavelengths, and to provide deeper starlight extinction by creating new designs for higher topological charge vortices. Within the VORTEX project, we also plan to develop new image processing techniques tailored to coronagraphic images, and to study some pre- and post-coronagraphic concepts adapted to the vortex coronagraph in order to reduce scattered starlight in the final images. [less ▲]

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See detailFirst prototypes of vortex retarders obtained by polarization holography
Piron, Pierre ULg; Blain, Pascal ULg; Décultot, Marc ULg et al

in Proceedings of SPIE (2014, May), 9099

This paper will present the first prototypes of vortex retarders made of photo-orientable liquid crystals polymers recorded without mechanical action using only polarization holography. Vortex retarders ... [more ▼]

This paper will present the first prototypes of vortex retarders made of photo-orientable liquid crystals polymers recorded without mechanical action using only polarization holography. Vortex retarders are birefringent plates characterized by a uniform phase retard and a rotation of their fast axis along their center. Liquid crystals are anisotropic molecules possessing birefringent properties. They are locally orientable and their orientation defines the fast axis orientation of the retarder. Their alignment depends on the local orientation of the recording electric field. The superimposition of several polarized beams will be used to shape the electric field to achieve the recording of vortex retarders. The mathematical aspects of the superimposition process, as well as several numerical simulations are exposed. Finally, the first prototypes are presented, characterized and compared to the numerical simulations. [less ▲]

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See detailSpace-variant optical phase retarders in liquid crystal polymers and their applications
Piron, Pierre ULg

Doctoral thesis (2014)

During the last decade, extensive investigations were performed to achieve optical phase retarders with a space-variant orientation of their fast axis. These retarders present unique behaviors and they ... [more ▼]

During the last decade, extensive investigations were performed to achieve optical phase retarders with a space-variant orientation of their fast axis. These retarders present unique behaviors and they can be used for several applications such as polarization analysis, beam splitting, phase mask coronagraphy, optical tweezers … The present thesis is dedicated to the development of space-variant retarders made out of liquid crystal polymers recorded by polarization holography. The liquid crystals define the fast axis orientation of the retarder. Polarization holography is based on the superimposition of differently polarized beams to achieve the electric field required to properly align the liquid crystals without mechanical action. In the present work, we start with an introduction about the space-variant retarders, their characteristics and current recording methods, which usually require mechanical action. In the second chapter, polarization holography and several simple examples are presented as well as the liquid crystal polymers, their generic recording process and the first prototypes. In chapter three, the first application that we developed is exposed. It consists in a polarization analysis method based on a retarder characterized by a variation in one dimension of its fast axis orientation. The principle of the method, numerical simulations and the first results are exposed. Chapter four cares about the second application based on a separator of polarization state. The mathematical model and its application to shearography are exposed. In chapter five, another kind of retarders is introduced. These retarders are characterized by a rotation of their fast axis along the center of the retarder. Their properties, the recording systems and the first prototypes are detailed and analyzed. In the last chapter, the application of our retarder to coronagraphy is presented and their performances are computed for different configurations based on experimental constrains. Finally, we conclude with the improvements of our applications and future uses of these retarders. [less ▲]

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See detailPolarization holography for vortex retarders recording
Piron, Pierre ULg; Blain, Pascal ULg; Mawet, Dimitri et al

in Applied Optics (2013), 52(28), 7040-7048

We present an original static recording method for vortex retarders (VRs) made from liquid crystal polymers (LCPs) using the superimposition of several polarized beams. VRs are birefringent plates ... [more ▼]

We present an original static recording method for vortex retarders (VRs) made from liquid crystal polymers (LCPs) using the superimposition of several polarized beams. VRs are birefringent plates characterized by a rotation of their fast axis about their center. The new method is based on polarization holography and photo-orientable LCP. Combining several polarized beams induces the polarization patterns required for the recording process of VRs without mechanical action. A mathematical description of the method, the outcomes of the numerical simulations, and the first experimental results are presented. [less ▲]

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See detailCombining shearography and interferometric fringe projection in a single device for complete control of industrial applications
Blain, Pascal ULg; Michel, Fabrice; Piron, Pierre ULg et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2013), 52(8), 0841021-7

Non-contact optical measurement methods are essential tools in many industrial and research domains. A family of new non-contact optical measurement methods based on the polarization states splitting ... [more ▼]

Non-contact optical measurement methods are essential tools in many industrial and research domains. A family of new non-contact optical measurement methods based on the polarization states splitting technique and monochromatic light projection as a way to overcome ambient lighting for in-situ measurement has been developed. Recent works on a birefringent element, a Savart plate, allow to build a more flexible and robust interferometer. This interferometer is a multipurpose metrological device. On one hand the interferometer can be set in front of a CCD camera. This optical measurement system is called a shearography interferometer and allows to measure micro displacements between two states of the studied object under coherent lighting. On the other hand by producing and shifting multiple sinusoidal Young’s interference patterns with this interferometer, and using a CCD camera, it is possible to build a 3D structured light profilometer. [less ▲]

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See detailAn in-line shearography setup based on circular polarization gratings
Blain, Pascal ULg; Piron, Pierre ULg; Renotte, Yvon ULg et al

in Optics & Lasers in Engineering (2013)

The shearing amount defines the resolution of a speckle shearing interferometer and the shearing direction defines the sensitivity direction of the setup. The properties of circular (cycloid) holographic ... [more ▼]

The shearing amount defines the resolution of a speckle shearing interferometer and the shearing direction defines the sensitivity direction of the setup. The properties of circular (cycloid) holographic polarization gratings recorded in liquid crystal polymers can be used to build a new multi-shearing direction and amount shearography setup. The polarization states of the diffracted beams offer an easy way to produce phase shifts and thus to compute the phase contained in the shearograms. The theoretical bases of such a device are highlighted and an original compact and full in-line setup is proposed. First experimental results of delamination detection and flaw detection by shearography are presented. A discussion on the importance of the grating recording and the polarization orientation points out the best working requirements. [less ▲]

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See detailInnovative Surface Plasmon Resonance biosensing architectures
Desfours, Caroline; Piron, Pierre ULg; Habraken, Serge ULg et al

Conference (2012, December 11)

Surface Plasmons Resonance (SPR) architectures involving multi-wavelength interrogation are an attractive alternative for droplet biosensing. We present our results for in situ measurements of biological ... [more ▼]

Surface Plasmons Resonance (SPR) architectures involving multi-wavelength interrogation are an attractive alternative for droplet biosensing. We present our results for in situ measurements of biological molecules with a two-wavelength sensor and a SPR Coupler-Disperser spectroscopic sensor. [less ▲]

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See detailPolarization Holography with liquid crystals polymers and applications
Piron, Pierre ULg; Blain, Pascal ULg; Habraken, Serge ULg et al

Conference (2012, December 10)

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized ... [more ▼]

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized. We present two applications polarization holography and coronagraphy [less ▲]

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See detailInnovative Surface Plasmon Resonance biosensing architectures
desfours, Caroline; Hastanin, Juriy ULg; Drucbert, Anne-Sophie et al

in International Conference on Fibre Optics and Photonics (2012, December)

Surface Plasmons Resonance (SPR) architectures involving multi-wavelength interrogation are an attractive alternative for droplet biosensing. We present our results for in situ measurements of biological ... [more ▼]

Surface Plasmons Resonance (SPR) architectures involving multi-wavelength interrogation are an attractive alternative for droplet biosensing. We present our results for in situ measurements of biological molecules with a two-wavelength sensor and a SPR Coupler- Disperser spectroscopic sensor. [less ▲]

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See detailPolarization Holography with liquid crystals polymers and applications
Piron, Pierre ULg; Blain, Pascal ULg; Habraken, Serge ULg et al

in International Conference on Fibre Optics and Photonics (2012, December)

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized ... [more ▼]

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized. We present two applications polarization holography and coronagraphy. [less ▲]

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See detailDéphaseurs en polymères à cristaux liquides pour la coronographie
Piron, Pierre ULg

Scientific conference (2012, May 22)

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See detailPhase retarders in liquid crystals polymers
Piron, Pierre ULg

Scientific conference (2012, March 12)

Liquid crystals polymers posses birefringent properties and they are locally orientable, they allow the realization of space variant optical retarders which creates non uniformly polarized beam. To ... [more ▼]

Liquid crystals polymers posses birefringent properties and they are locally orientable, they allow the realization of space variant optical retarders which creates non uniformly polarized beam. To realize a retarder, liquid crystals are exposed to a UV linearly polarized beam, the optical axis of the retarder will be parallel to the incident polarization. We shall present an innovative way to produce space-variant retarders without mechanical interaction polarization holography . Superposing several beams differently polarized, results in a non-uniformly polarized recording beam used to realize space variant retarders. We shall also present our research retarders for two applications based on this method polarization analysis and coronagraphy. [less ▲]

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See detailTaking the vector vortex coronagraph to the next level for ground- and space-based exoplanet imaging instruments: review of technology developments in the USA, Japan, and Europe
Mawet, Dimitri; Murakami, Naoshi; Delacroix, Christian ULg et al

in Shaklan, Stuart (Ed.) Techniques and Instrumentation for Detection of Exoplanets V. (2011, September 01)

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at ... [more ▼]

The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris- Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive optics, extremely large ground-based telescopes, and space-based internal coronagraphs. [less ▲]

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See detailPolarization measurement with space-variant retarders in liquid crystal polymers
Piron, Pierre ULg; Blain, Pascal ULg; Habraken, Serge ULg

in SPIE proceedings 8160, SPIE Optics +Photonics 2011 San Diego (2011)

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis ... [more ▼]

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis orientation. The method computes the Stokes parameters of an incident beam by studying the intensity distribution after the retarder and a linear polarizer. This paper contains the mathematical modelization, the numerical simulation, the description of the experimental setup, the results for several completely polarized beams and the future developments of this method. [less ▲]

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See detailSimulations of coronagraphy with a dynamic hologram for the direct detection of exo-planets
Ricci, Davide ULg; Le Coroller, Hervé; Labeyrie, Antoine et al

in Oschmann, J, Clampin, M. (Ed.) Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave (2010)

In a previous paper, we discussed an original solution to improve the performances of coronagraphs by adding, in the optical scheme, an adaptive hologram removing most of the residual speckle starlight ... [more ▼]

In a previous paper, we discussed an original solution to improve the performances of coronagraphs by adding, in the optical scheme, an adaptive hologram removing most of the residual speckle starlight. In our simulations, the detection limit in the flux ratio between a host star and a very near planet (5λ/D) improves over a factor 1 000 (resp. 10 000) when equipped with a hologram for cases of wavefront bumpiness imperfections of λ/20 (resp. λ/100). We derive, in this paper, the transmission accuracy required on the hologram pixels to achieve such goals. We show that preliminary tests could be performed on the basis of existing technologies. [less ▲]

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See detailBanc polarimétrique de mesure de masques de phase pour la coronographie
Piron, Pierre ULg

Master's dissertation (2009)

Ce travail comprend deux parties. La première partie replace la coronographie dans son contexte historique (détection des exoplanètes) et scientifique (différentes théories physiques et leur développement ... [more ▼]

Ce travail comprend deux parties. La première partie replace la coronographie dans son contexte historique (détection des exoplanètes) et scientifique (différentes théories physiques et leur développement mathématique). Elle présente les qualités et les défauts des différents masques utilisés dans les coronographes. A l’origine, la coronographie est une technique utilisée en astronomie pour reproduire une éclipse totale de soleil. Depuis la découverte de la première exoplanète en 1995, la coronographie est en pleine (r)évolution : elle s’efforce de donner une image d’un compagnon faible qui orbite autour d’une étoile brillante. Grâce à la spectroscopie, une image peut fournir des informations inaccessibles aux autres méthodes de détection (présence d’eau, de vie, ...). La chromaticité (dépendance à la longueur d’onde de travail) est le défaut le plus gênant pour un masque coronographique ; les chercheurs rivalisent donc d’ingéniosité pour améliorer sans cesse les performances et repousser toujours plus loin les limites instrumentales. Dans les années 2000, les masque de phase apparaissent : ils produisent un déphasage soit par différence de chemin optique (masques chromatiques : DPM, 4QPM) soit par opposition de phase entre les composantes électrique et magnétique de la lumière (masques achromatiques : 4QAPS, 4ZOG, AGPM). L’interférence destructive due au déphasage provoque l’atténuation totale ou partielle d’une source lumineuse centrée (une étoile). Par contre, la lumière d’une source décentrée (une étoile faible voisine, une planète qui orbite autour de l’étoile) n’est pas ou peu atténuée. Ce principe explique le rôle joué par la coronographie dans la détection des exoplanètes. Grâce à leur biréfringence de forme, les réseaux sublambda de type ZOG créent une différence de phase entre les composantes électrique et magnétique de la lumière. Le masque de phase à quatre quadrants 4ZOG est formé de quatre ZOGs orientés pour créer une opposition de phase entre deux quadrants adjacents. L’Annular Groove Phase Mask (AGPM) est un réseau ZOG "space-variant" qui génère un vortex optique avec une interférence destructive au centre. L’optimisation de la configuration spatiale d’un ZOG (pas du réseau, profondeur de gravure, facteur de remplissage, ...) améliore ses performances optiques mais une erreur sur le déphasage est toujours possible. Elle est due au manque de précision lors de la fabrication par lithographie. Le défi actuel à relever est de trouver une technologie de fabrication plus fiable : les Liquid Crystal Polymers semblent prometteurs. La deuxième partie est plus pratique : elle présente le banc de mesure mis au point à l’Hololab de la Faculté des Sciences de l’Université de Liège. Il est prévu pour travailler dans les bandes infrarouges H et K qui sont couramment utilisées en astronomie, notamment pour la détection des exoplanètes. Il est destiné à mesurer le déphasage produit par les retardateurs de phase (phase shifters), entre autres, les masques de phase utilisés en coronographie : des plus simples (lames quart d’onde, lames demi-ondes) aux plus sophistiqués (masques de phase de type ZOG) en passant par les rhomboèdres de Fresnel (réflection totale interne). Cette partie décrit les différents composants et leur mise au point initiale, le principe polarimétrique de son fonctionnement, le programme LabVIEW qui commande les polariseurs mobiles et la prise de mesure par le détecteur, les modules MATLAB qui traitent les données, les limites actuelles à son fonctionnement (vitesse de fonctonnement, précision des mesures, stabilité des mesures, ...) Un chapitre présente les résultats expérimentaux obtenus pour quelques échantillons testés : une lame quart d’onde avec le laser à 1.55 m, la même lame avec le laser à 2.3 m, un rhomboèdre de Fresnel avec le laser à 1.55 m. [less ▲]

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See detailCoronography with a dynamic hologram
Ricci, Davide ULg; Le Coroller, Hervé; Piron, Pierre ULg

Poster (2008, September 26)

An innovative solution to improve the performances of coronagraphs consists in adding, in the optical scheme, a dynamic hologram removing most of the residual speckle starlight. Our simulations show that ... [more ▼]

An innovative solution to improve the performances of coronagraphs consists in adding, in the optical scheme, a dynamic hologram removing most of the residual speckle starlight. Our simulations show that the detection limit in the flux ratio between a host star and a very near planet, in the case of wavefront bumpiness imperfections at lambda/20 (resp. lambda/100), improves over a factor 1000 (resp. 10000) when equipped with a hologram, allowing to direct image an exo-Earth at a distance of 11 parsec with a 6.5m space telescope. [less ▲]

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