References of "Mawet, Dimitri"      in Complete repository Arts & humanities   Archaeology   Art & art history   Classical & oriental studies   History   Languages & linguistics   Literature   Performing arts   Philosophy & ethics   Religion & theology   Multidisciplinary, general & others Business & economic sciences   Accounting & auditing   Production, distribution & supply chain management   Finance   General management & organizational theory   Human resources management   Management information systems   Marketing   Strategy & innovation   Quantitative methods in economics & management   General economics & history of economic thought   International economics   Macroeconomics & monetary economics   Microeconomics   Economic systems & public economics   Social economics   Special economic topics (health, labor, transportation…)   Multidisciplinary, general & others Engineering, computing & technology   Aerospace & aeronautics engineering   Architecture   Chemical engineering   Civil engineering   Computer science   Electrical & electronics engineering   Energy   Geological, petroleum & mining engineering   Materials science & engineering   Mechanical engineering   Multidisciplinary, general & others Human health sciences   Alternative medicine   Anesthesia & intensive care   Cardiovascular & respiratory systems   Dentistry & oral medicine   Dermatology   Endocrinology, metabolism & nutrition   Forensic medicine   Gastroenterology & hepatology   General & internal medicine   Geriatrics   Hematology   Immunology & infectious disease   Laboratory medicine & medical technology   Neurology   Oncology   Ophthalmology   Orthopedics, rehabilitation & sports medicine   Otolaryngology   Pediatrics   Pharmacy, pharmacology & toxicology   Psychiatry   Public health, health care sciences & services   Radiology, nuclear medicine & imaging   Reproductive medicine (gynecology, andrology, obstetrics)   Rheumatology   Surgery   Urology & nephrology   Multidisciplinary, general & others Law, criminology & political science   Civil law   Criminal law & procedure   Criminology   Economic & commercial law   European & international law   Judicial law   Metalaw, Roman law, history of law & comparative law   Political science, public administration & international relations   Public law   Social law   Tax law   Multidisciplinary, general & others Life sciences   Agriculture & agronomy   Anatomy (cytology, histology, embryology...) & physiology   Animal production & animal husbandry   Aquatic sciences & oceanology   Biochemistry, biophysics & molecular biology   Biotechnology   Entomology & pest control   Environmental sciences & ecology   Food science   Genetics & genetic processes   Microbiology   Phytobiology (plant sciences, forestry, mycology...)   Veterinary medicine & animal health   Zoology   Multidisciplinary, general & others Physical, chemical, mathematical & earth Sciences   Chemistry   Earth sciences & physical geography   Mathematics   Physics   Space science, astronomy & astrophysics   Multidisciplinary, general & others Social & behavioral sciences, psychology   Animal psychology, ethology & psychobiology   Anthropology   Communication & mass media   Education & instruction   Human geography & demography   Library & information sciences   Neurosciences & behavior   Regional & inter-regional studies   Social work & social policy   Sociology & social sciences   Social, industrial & organizational psychology   Theoretical & cognitive psychology   Treatment & clinical psychology   Multidisciplinary, general & others     Showing results 1 to 20 of 40 1 2 3     Post-coronagraphic tip-tilt sensing for vortex phase masks: the QACITS techniqueHuby, Elsa ; Baudoz, Pierre; Mawet, Dimitri et alin Astronomy and Astrophysics (2015), 584Small inner working angle coronagraphs, like the vortex phase mask, are essential to exploit the full potential of ground-based telescopes in the context of exoplanet detection and characterization ... [more ▼]Small inner working angle coronagraphs, like the vortex phase mask, are essential to exploit the full potential of ground-based telescopes in the context of exoplanet detection and characterization. However, the drawback of this attractive feature is a high sensitivity to pointing errors, which degrades the performance of the coronagraph. We propose a tip-tilt retrieval technique based on the analysis of the final coronagraphic image, hereafter called Quadrant Analysis of Coronagraphic Images for Tip-tilt Sensing (QACITS). Under the assumption of small phase aberrations, we show that the behaviour of the vortex phase mask can be simply described from the entrance pupil to the Lyot stop plane by Zernike polynomials. This convenient formalism is used to establish the theoretical basis of the QACITS technique. Simulations have been performed to demonstrate the validity and limits of the technique, including the case of a centrally obstructed pupil. The QACITS technique principle is further validated by experimental results in the case of an unobstructed circular aperture. The typical configuration of the Keck telescope (24% central obstruction) has been simulated with additional high order aberrations. In these conditions, our simulations show that the QACITS technique is still adapted to centrally obstructed pupils and performs tip-tilt retrieval with a precision of $5 \times 10^{-2}$ {\lambda}/D when wavefront errors amount to {\lambda}/14 rms and $10^{-2}$ {\lambda}/D for {\lambda}/70 rms errors (with {\lambda} the wavelength and D the pupil diameter). The implementation of the QACITS technique is based on the analysis of the scientific image and does not require any modification of the original setup. Current facilities equipped with a vortex phase mask can thus directly benefit from this technique to improve the contrast performance close to the axis. [less ▲]Detailed reference viewed: 29 (11 ULg) Lyot-plane phase masks for improved high-contrast imaging with a vortex coronagraphRuane, Garreth J.; Huby, Elsa ; Absil, Olivier et alin Astronomy and Astrophysics (2015), 583The vortex coronagraph is an optical instrument that precisely removes on-axis starlight allowing for high contrast imaging at small angular separation from the star, thereby providing a crucial ... [more ▼]The vortex coronagraph is an optical instrument that precisely removes on-axis starlight allowing for high contrast imaging at small angular separation from the star, thereby providing a crucial capability for direct detection and characterization of exoplanets and circumstellar disks. Telescopes with aperture obstructions, such as secondary mirrors and spider support structures, require advanced coronagraph designs to provide adequate starlight suppression. We introduce a phase-only Lyot-plane optic to the vortex coronagraph that offers improved contrast performance on telescopes with complicated apertures. Potential solutions for the European Extremely Large Telescope (E-ELT) are described and compared. Adding a Lyot-plane phase mask relocates residual starlight away from a region of the image plane thereby reducing stellar noise and improving sensitivity to off-axis companions. The phase mask is calculated using an iterative phase retrieval algorithm. Numerically, we achieve a contrast on the order of $10^{-6}$ for a companion with angular displacement as small as $4~\lambda/D$ with an E-ELT type aperture. Even in the presence of aberrations, improved performance is expected compared to either a conventional vortex coronagraph or optimized pupil plane phase element alone. [less ▲]Detailed reference viewed: 32 (5 ULg) Optimized focal and pupil plane masks for vortex coronagraphs on telescopes with obstructed aperturesRuane, Garreth; Absil, Olivier ; Huby, Elsa et alin Shaklan, Stuart (Ed.) Techniques and Instrumentation for Detection of Exoplanets VII (2015, September 11)We present methods for optimizing pupil and focal plane optical elements that improve the performance of vortex coronagraphs on telescopes with obstructed or segmented apertures. Phase-only and complex ... [more ▼]We present methods for optimizing pupil and focal plane optical elements that improve the performance of vortex coronagraphs on telescopes with obstructed or segmented apertures. Phase-only and complex masks are designed for the entrance pupil, focal plane, and the plane of the Lyot stop. Optimal masks are obtained using both analytical and numerical methods. The latter makes use of an iterative error reduction algorithm to calculate "correcting" optics that mitigate unwanted diffraction from aperture obstructions. We analyze the achieved performance in terms of starlight suppression, contrast, off-axis image quality, and chromatic dependence. Manufacturing considerations and sensitivity to aberrations are also discussed. This work provides a path to joint optimization of multiple coronagraph planes to maximize sensitivity to exoplanets and other faint companions. [less ▲]Detailed reference viewed: 29 (10 ULg) A Mach-Zehnder interferometer based on orbital angular momentum for improved vortex coronagraph efficiencyPiron, Pierre ; Delacroix, Christian; Huby, Elsa et alin Shaklan, Stuart (Ed.) Techniques and Instrumentation for Detection of Exoplanets VII (2015, September 11)The Annular Groove Phase Mask (AGPM) is a vectorial vortex phase mask. It acts as a half-wave plate with a radial fast axis orientation operating in the mid infrared domain. When placed at the focus of a ... [more ▼]The Annular Groove Phase Mask (AGPM) is a vectorial vortex phase mask. It acts as a half-wave plate with a radial fast axis orientation operating in the mid infrared domain. When placed at the focus of a telescope element provides a continuous helical phase ramp for an on axis sources, which creates the orbital angular momentum. Thanks to that phase, the intensity of the central source is canceled by a down-stream pupil stop, while the off axis sources are not affected. However due to experimental conditions the nulling is hardly perfect. To improve the null, a Mach-Zehnder interferometer containing Dove prisms differently oriented can be proposed to sort out light based on its orbital angular momentum (OAM). Thanks to the differential rotation of the beam, a π phase shift is achieved for the on axis light affected by a non zero OAM. Therefore the contrast between the star and its faint companion is enhanced. Nevertheless, due the Dove prisms birefringence, the performance of the interferometer is relatively poor. To solve this problem, we propose to add a birefringent wave-plate in each arm to compensate this birefringence. In this paper, we will develop the mathematical model of the wave front using the Jones formalism. The performance of the interferometer is at first computed for the simple version without the birefringent plate. Then the effect of the birefringent plate is be mathematically described and the performance is re-computed. [less ▲]Detailed reference viewed: 28 (8 ULg) Polarization holography for vortex retarders recording: laboratory demonstrationPiron, Pierre ; Blain, Pascal ; Décultot, Marc et alin Applied Optics (2015), 54(15), 4765--4770This paper will present a prototype of the first set of vortex retarders made of liquid crystal polymers recorded by polarization holography. Vortex retarders are birefringent plates characterized by a ... [more ▼]This paper will present a prototype of the first set of vortex retarders made of liquid crystal polymers recorded by polarization holography. Vortex retarders are birefringent plates characterized by a rotation of their fast axis. Liquid crystals possess birefringent properties and they are locally orientable. Their orientation is defined by the perpendicular to the local orientation of the recording field. Polarization holography is a purely optical recording method. It is based on the superimposition of coherent and differently polarized beams. It is used to shape the electric field pattern to enable the recording of vortex retarders. The paper details the mathematical model of the superimposition process. The recording setup is exposed; it is characterized by a nearly common path interferometer. Two sets of measurements allowing the prediction of the retarder’s features are presented and compared. Finally, the experimentally recorded retarder is shown, its characteristics are investigated and compared to the predicted ones. [less ▲]Detailed reference viewed: 31 (17 ULg) Discovery of a Companion Candidate in the HD 169142 Transition Disk and the Possibility of Multiple Planet FormationReggiani, Maddalena; Quanz, Sascha P.; Meyer, Michael R. et alin Astrophysical Journal Letters (2014), 792We present L'- and J-band high-contrast observations of HD 169142, obtained with the Very Large Telescope/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager, respectively. A source located ... [more ▼]We present L'- and J-band high-contrast observations of HD 169142, obtained with the Very Large Telescope/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager, respectively. A source located at 0.''156 ± 0.''032 north of the host star (P.A. = 7.4° ± 11.3°) appears in the final reduced L' image. At the distance of the star (~145 pc), this angular separation corresponds to a physical separation of 22.7 ± 4.7 AU, locating the source within the recently resolved inner cavity of the transition disk. The source has a brightness of L' = 12.2 ± 0.5 mag, whereas it is not detected in the J band (J >13.8 mag). If its L' brightness arose solely from the photosphere of a companion and given the J - L' color constraints, it would correspond to a 28-32 MJup object at the age of the star, according to the COND models. Ongoing accretion activity of the star suggests, however, that gas is left in the inner disk cavity from which the companion could also be accreting. In this case, the object could be lower in mass and its luminosity enhanced by the accretion process and by a circumplanetary disk. A lower-mass object is more consistent with the observed cavity width. Finally, the observations enable us to place an upper limit on the L'-band flux of a second companion candidate orbiting in the disk annular gap at ~50 AU, as suggested by millimeter observations. If the second companion is also confirmed, HD 169142 might be forming a planetary system, with at least two companions opening gaps and possibly interacting with each other. [less ▲]Detailed reference viewed: 24 (5 ULg) Realizing the diamond annular groove phase masks for the mid infrared region: five years of successful process development of diamond plasma etchingForsberg, Pontus; Vargas Catalan, Ernesto; Delacroix, Christian et alin Navarro, Ramon; Cunningham, Colin; Barto, Allison (Eds.) Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation (2014, August 07)The Annular Groove Phase Mask (AGPM) is a circularly symmetric half wave plate consisting of a circular high aspect ratio sub-wavelength grating. Here we present a method for realizing such structures in ... [more ▼]The Annular Groove Phase Mask (AGPM) is a circularly symmetric half wave plate consisting of a circular high aspect ratio sub-wavelength grating. Here we present a method for realizing such structures in diamond. To improve the AGPM performance, antireflective sub-wavelength gratings are etched on the backside of the components, and such gratings are also discussed. Components for the N-band (around 10 μm) and the L-band (around 3.8 μm) have been successfully fabricated. We are currently developing the process further to improve the precision of the gratings and produce an AGPM for the K-band (around 2.2 μm). © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. [less ▲]Detailed reference viewed: 23 (2 ULg) The VORTEX project: first results and perspectivesAbsil, Olivier ; Mawet, Dimitri; Delacroix, Christian et alin Marchetti, Enrico; Close, Laird; Véran, Jean-Pierre (Eds.) Adaptive Optics Systems IV (2014, July 21)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 ▲]Detailed reference viewed: 98 (42 ULg) The VORTEX coronagraphic test benchJolivet, Aïssa ; Piron, Pierre ; Huby, Elsa et alin Navarro, Ramon; Cunningham, Colin; Barto, Allison (Eds.) Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation (2014, July 18)In this paper, we present the infrared coronagraphic test bench of the University of Liège named VODCA (Vortex Optical Demonstrator for Coronagraphic Applications). The goal of the bench is to assess the ... [more ▼]In this paper, we present the infrared coronagraphic test bench of the University of Liège named VODCA (Vortex Optical Demonstrator for Coronagraphic Applications). The goal of the bench is to assess the performances of the Annular Groove Phase Masks (AGPMs) at near- to mid-infrared wavelengths. The AGPM is a subwavelength grating vortex coronagraph of charge two (SGVC2) made out of diamond. The bench is designed to be completely achromatic and will be composed of a super continuum laser source emitting in the near to mid-infrared, several parabolas, diaphragms and an infrared camera. This way, we will be able to test the different AGPMs in the M, L, K and H bands. Eventually, the bench will also allow the computation of the incident wavefront aberrations on the coronagraph. A reflective Lyot stop will send most of the stellar light to a second camera to perform low-order wavefront sensing. This second system coupled with a deformable mirror will allow the correction of the wavefront aberrations. We also aim to test other pre- and/or post-coronagraphic concepts such as optimal apodization. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. [less ▲]Detailed reference viewed: 31 (10 ULg) Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4)Delacroix, Christian ; Absil, Olivier ; Carlomagno, Brunella et alin Ramsay, Suzanne; McLean, Ian; Takami, Hideki (Eds.) Ground-based and Airborne Instrumentation for Astronomy V (2014, July 08)One possible solution to achieve high contrast direct imaging at a small inner working angle (IWA) is to use a vector vortex coronagraph (VVC), which provides a continuous helical phase ramp in the focal ... [more ▼]One possible solution to achieve high contrast direct imaging at a small inner working angle (IWA) is to use a vector vortex coronagraph (VVC), which provides a continuous helical phase ramp in the focal plane of the telescope with a phase singularity in its center. Such an optical vortex is characterized by its topological charge, i.e., the number of times the phase accumulates 2pi radians along a closed path surrounding the singularity. Over the past few years, we have been developing a charge-2 VVC induced by rotationally symmetric subwavelength gratings (SGVC2), also known as the Annular Groove Phase Mask (AGPM). Since 2013, several SGVC2s (or AGPMs) were manufactured using synthetic diamond substrate, then validated on dedicated optical benches, and installed on 10-m class telescopes. Increasing the topological charge seems however mandatory for cancelling the light of bright stars which will be partially resolved by future Extremely Large Telescopes in the near-infrared. In this paper, we first detail our motivations for developing an SGVC4 (charge 4) dedicated to the near-infrared domain. The challenge lies in the design of the pattern which is unrealistic in the theoretically perfect case, due to state-of-the-art manufacturing limitations. Hence, we propose a new realistic design of SGVC4 with minimized discontinuities and optimized phase ramp, showing conclusive improvements over previous works in this field. A preliminary validation of our concept is given based on RCWA simulations, while full 3D finite-difference time-domain simulations (and eventually laboratory tests) will be required for a final validation. [less ▲]Detailed reference viewed: 23 (5 ULg) Mid-IR AGPMs for ELT applicationsCarlomagno, Brunella ; Delacroix, Christian ; Absil, Olivier et alin Ramsay, Suzanne; McLean, Ian; Takami, Hideki (Eds.) Ground-based and Airborne Instrumentation for Astronomy V (2014, July 08)The mid-infrared region is well suited for exoplanet detection thanks to the reduced contrast between the planet and its host star with respect to the visible and near-infrared wavelength regimes. This ... [more ▼]The mid-infrared region is well suited for exoplanet detection thanks to the reduced contrast between the planet and its host star with respect to the visible and near-infrared wavelength regimes. This contrast may be further improved with Vector Vortex Coronagraphs (VVCs), which allow us to cancel the starlight. One flavour of the VVC is the AGPM (Annular Groove Phase Mask), which adds the interesting properties of subwavelength gratings (achromaticity, robustness) to the already known properties of the VVC. In this paper, we present the optimized designs, as well as the expected performances of mid-IR AGPMs etched onto synthetic diamond substrates, which are considered for the E-ELT/METIS instrument. [less ▲]Detailed reference viewed: 37 (7 ULg) First High-Angular Resolution L' Images of the β Pictoris Debris Disc with the VLT / NaCoMilli, Julien; Mawet, Dimitri; Absil, Olivier et alin Booth, Mark; Matthews, Brenda; Graham, James (Eds.) Exploring the Formation and Evolution of Planetary Systems (2014, January 01)Imaging debris discs in the L'-band (3.8 μm) is a difficult task. Quasi-static speckles from imperfect optics prevail below 1'' whereas background emission is the dominant noise source beyond that ... [more ▼]Imaging debris discs in the L'-band (3.8 μm) is a difficult task. Quasi-static speckles from imperfect optics prevail below 1'' whereas background emission is the dominant noise source beyond that separation and is much larger than at shorter wavelengths. We demonstrate here the potential of the newly commissioned AGPM coronograph on VLT/NaCo combined with advanced star and sky subtraction technique based on Principal Component Analysis, and we analyze the morphology of the β Pictoris disc. [less ▲]Detailed reference viewed: 19 (2 ULg) Polarization holography for vortex retarders recordingPiron, Pierre ; Blain, Pascal ; Mawet, Dimitri et alin Applied Optics (2013), 52(28), 7040-7048We 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 ▲]Detailed reference viewed: 47 (19 ULg) Small-angle, high-contrast exoplanet imaging with the L-band AGPM vector vortex coronagraph now offered at the VLTMawet, Dimitri; Absil, Olivier ; Milli, Julien et alin Shaklan, Stuart (Ed.) Techniques and Instrumentation for Detection of Exoplanets VI (2013, September 26)In November 2012, we installed an L-band annular groove phase mask (AGPM) vector vortex coronagraph (VVC) inside NACO, the adaptive optics camera of ESO's Very Large Telescope. The mask, made out of ... [more ▼]In November 2012, we installed an L-band annular groove phase mask (AGPM) vector vortex coronagraph (VVC) inside NACO, the adaptive optics camera of ESO's Very Large Telescope. The mask, made out of diamond subwavelength gratings has been commissioned, science qualified, and is now offered to the community. Here we report ground-breaking on-sky performance levels in terms of contrast, inner working angle, and discovery space. This new practical demonstration of the VVC, coming a few years after Palomar's and recent record-breaking lab experiments in the visible (E. Serabyn et al. 2013, these proceedings), shows once again that this new-generation coronagraph has reached a high level of maturity. [less ▲]Detailed reference viewed: 21 (3 ULg) Laboratory demonstration of a mid-infrared AGPM vector vortex coronagraphDelacroix, Christian ; Absil, Olivier ; Forsberg, Pontus et alin Astronomy and Astrophysics (2013), 553Coronagraphy is a powerful technique to achieve high contrast imaging and hence to image faint companions around bright targets. Various concepts have been used in the visible and near-infrared regimes ... [more ▼]Coronagraphy is a powerful technique to achieve high contrast imaging and hence to image faint companions around bright targets. Various concepts have been used in the visible and near-infrared regimes, while coronagraphic applications in the mid-infrared remain nowadays largely unexplored. Vector vortex phase masks based on concentric subwavelength gratings show great promise for such applications. We aim at producing and validating the first high-performance broadband focal plane phase mask coronagraphs for applications in the mid-infrared regime, and in particular the L band with a fractional bandwidth of ~16% (3.5-4.1 \mu m). Based on rigorous coupled wave analysis, we designed an annular groove phase mask (AGPM) producing a vortex effect in the L band, and etched it onto a series of diamond substrates. The grating parameters were measured by means of scanning electron microscopy. The resulting components were then tested on a mid-infrared coronagraphic test bench. A broadband raw null depth of 2 x 10^{-3} was obtained for our best L-band AGPM after only a few iterations between design and manufacturing. This corresponds to a raw contrast of about 6 x 10^{-5} (10.5 mag) at 2\lambda/D. This result is fully in line with our projections based on rigorous coupled wave analysis modeling, using the measured grating parameters. The sensitivity to tilt and focus has also been evaluated. After years of technological developments, mid-infrared vector vortex coronagraphs finally become a reality and live up to our expectations. Based on their measured performance, our L-band AGPMs are now ready to open a new parameter space in exoplanet imaging at major ground-based observatories. [less ▲]Detailed reference viewed: 60 (21 ULg) Polarization Holography with liquid crystals polymers and applicationsPiron, Pierre ; Blain, Pascal ; Habraken, Serge et alConference (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 ▲]Detailed reference viewed: 23 (5 ULg) Polarization Holography with liquid crystals polymers and applicationsPiron, Pierre ; Blain, Pascal ; Habraken, Serge et alin 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 ▲]Detailed reference viewed: 32 (5 ULg) Design, manufacturing, and performance analysis of mid-infrared achromatic half-wave plates with diamond subwavelength gratingsDelacroix, Christian ; Forsberg, Pontus; Karlsson, Mikael et alin Applied Optics (2012), 51In this paper, we present an elegant solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out ... [more ▼]In this paper, we present an elegant solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out of diamond. We use the rigorous coupled wave analysis to design the gratings. Our analysis shows that diamond, besides its outstanding physical and mechanical properties, is a suitable substrate to manufacture mid-infrared HWPs, thanks to its high refractive index which allows etching SWGs with lower aspect ratio. Based on our optized design, we manufactured a diamond HWP for the 11-13.2 µm region, with an estimated mean retardance ~3.143 ± 0.061 rad (180.08 ± 3.51°). In addition, an antireflective grating was etched on the backside of the wave plate, allowing a total tansmittance between 89 and 95% over the band. [less ▲]Detailed reference viewed: 70 (15 ULg) Direct imaging of extra-solar planets in star forming regions. Lessons learned from a false positive around IM Lup.Mawet, Dimitri; Absil, Olivier ; Riaud, Pierre et alin Astronomy and Astrophysics (2012), 544Context. Most planet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the ... [more ▼]Context. Most planet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the near-infrared window (1 - 5 µm). Because of these practical limitations, our current observational aim at detecting and characterizing planets puts heavy constraints on target selection, observing strategies, data reduction, and follow-up. Most surveys so far have thus targeted very young systems (1 - 100Myr) to catch the putative remnant thermal radiation of giant planets, which peaks in the near-infrared. They also favor systems in the solar neighborhood (d < 80 pc), which eases angular resolution requirements but also ensures a good knowledge of the distance and proper motion, which are critical to secure the planet status, and enable any subsequent characterization. Aims. Because of their youth, it is very tempting to target the nearby star forming regions, which are typically twice as far as the bulk of objects usually combed for planets by direct imaging. Probing these very interesting reservoirs in practice sets additional constraints that we review in this paper by presenting the planet search that we initiated in 2008 around the disk-bearing T Tauri star IM Lup, which is part of the Lupus star forming region (140-190 pc). Methods. We show and discuss why age determination, the choice of evolutionary model for both the central star and the planet, precise knowledge of the host star proper motion, relative or absolute (between different instruments) astrometric accuracy (including plate scale calibration), and patience are the key ingredients for exoplanet searches around more distant young stars. Results. Unfortunately, most of the time, precision and perseverance are not paying off: we discovered a candidate companion around IM Lup in 2008, which we report here to be a false positive event. We nevertheless review in details the lessons learned from our endeavor, and additionally present the best detection limits ever calculated for IM Lup. We also accessorily report on the successful use of innovative data reduction techniques, such as the damped-LOCI and iterative roll subtraction. [less ▲]Detailed reference viewed: 70 (4 ULg) A diamond AGPM coronagraph for VISIRDelacroix, Christian ; Absil, Olivier ; Mawet, Dimitri et alin McLean, I; Ramsay, S; Takami, H (Eds.) Ground-based and Airborne Instrumentation for Astronomy IV (2012, July 05)In recent years, phase mask coronagraphy has become increasingly efficient in imaging the close environment of stars, enabling the search for exoplanets and circumstellar disks. Coronagraphs are ideally ... [more ▼]In recent years, phase mask coronagraphy has become increasingly efficient in imaging the close environment of stars, enabling the search for exoplanets and circumstellar disks. Coronagraphs are ideally suited instruments, characterized by high dynamic range imaging capabilities, while preserving a small inner working angle. The AGPM (Annular Groove Phase Mask, Mawet et al. 20051) consists of a vector vortex induced by a rotationally symmetric subwavelength grating. This technique constitutes an almost unique solution to the achromatization at longer wavelengths (mid-infrared). For this reason, we have specially conceived a mid-infrared AGPM coronagraph for the forthcoming upgrade of VISIR, the mid-IR imager and spectrograph on the VLT at ESO (Paranal), in collaboration with members of the VISIR consortium. The implementation phase of the VISIR Upgrade Project is foreseen for May-August 2012, and the AGPM installed will cover the 11-13.2 μm spectral range. In this paper, we present the entire fabrication process of our AGPM imprinted on a diamond substrate. Diamond is an ideal material for mid-infrared wavelengths owing to its high transparency, small dispersion, extremely low thermal expansion and outstanding mechanical and chemical properties. The design process has been performed with an algorithm based on the rigorous coupled wave analysis (RCWA), and the micro-fabrication has been carried out using nano-imprint lithography and reactive ion etching. A precise grating profile metrology has also been conducted using cleaving techniques. Finally, we show the deposit of fiducials (i.e. centering marks) with Aerosol Jet Printing (AJP). We conclude with the ultimate coronagraph expected performances. [less ▲]Detailed reference viewed: 53 (11 ULg) 1 2 3