Simulations of coronagraphy with a dynamic hologram for the direct detection of exo-planets

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 (5 lambda/D) improves over a factor 1000 (resp. 10000) when equipped with a hologram for cases of wavefront bumpiness imperfections of lambda/20 (resp. lambda/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.Comment: 5 pages, 6 figure

Pratiques de publication, dépôt institutionnel et perception du libre accès : enquête auprès des chercheuses et chercheurs de l’Université Laval (Québec)

Afin de mieux comprendre les pratiques de publication des chercheuses et chercheurs de l'Université Laval, ainsi que leur compréhension du droit d'auteur et du libre accès, une enquête Web a été réalisée au printemps 2014 par un comité de la Bibliothèque qui réfléchit à l'implantation d'un dépôt institutionnel. Plus de la m oitié des 637 répondantes et répondants font partie du corps professoral, alors que 22 % sont rattachés à la Faculté des sciences et de génie, 18% à la Faculté de médecine et 15% à la Faculté des sciences sociales. La plupart de ces personnes sont membres de réseaux sociaux scientifiques dans le but d'être en contact avec des pairs et d'assurer le développement de leur rayonnement international. Leurs publications sont majoritairement évaluées par des pairs. L'enquête révèle que le mouvement du libre accès commence à être connu dans la communauté universitaire. Plusieurs répondantes et répondants témoignent de débats au sujet du libre accès dans les comités de rédaction de revues scientifiques, qu'elles soient ou non engagées dans le libre accès. Toutefois, une grande majorité de personnes s'estiment mal informées sur la question du libre accès; plusieurs reconnaissent avoir plutôt des impressions ou des croyances qu'une connaissance claire des pratiques et des enjeux du libre accès, notamment des possibilit és d'archivage institutionnel d'articles déjà publiés. Leur connaissance du sujet est principalement due à des informations glanées lors de lectures ou d'échanges entre collègues. Les lieux plus formels comme les colloques ou les ressources institutionnell es comme les bibliothécaires ont peu d'impact. Cette situation peut expliquer la présence de plusieurs fausses croyances ou « mythes » parmi les commentaires recueillis, en particulier à propos des frais exigés des auteurs par les revues scientifiques en l ibre accès : contrairement à ce que rapportent plusieurs, cette situation n'est le cas que de 30% des revues en libre accès. De la même manière, une partie des répondantes et répondants estiment que les revues scientifiques interdisent aux auteurs d'auto - archiver leurs articles publiés, ce qui est faux, puisque la plupart des revues le permettent, parfois après un certain délai. Certaines réponses assimilent « publication en ligne » et « publication en libre accès ». L'enquête a également révélé un paradoxe déjà constaté dans d'autres enquêtes canadiennes ou internationales : sur le plan des principes, les chercheuses et chercheurs sont presque tous en faveur du libre accès, mais n'en font pas un critère important lors de leur choix d'une revue pour leurs pu blications. Les critères de notoriété ou d'impact sont les plus décisifs, et de loin. En matière de droit d'auteur, les réponses témoignent d'une méconnaissance des droits des auteurs et des outils pour les préserver (négociation avec la maison d'édition, licences Creative Commons, addendum de SPARC). Cette situation place de nombreux chercheuses et chercheurs dans une position de vulnérabilité face aux exigences des 5 revues scientifiques commerciales et surtout dans l'ignorance de leur droit à auto - archiver leurs publications. Les pratiques d'auto - archivage qui ont été rapportées sont discrètes : la majorité des chercheurs et chercheuses qui ont participé à l'enquête conservent une copie de leurs travaux sur leur ordinateur personnel, mais ne les diffusent q ue sur demande ou en envoyant un lien hypertexte vers leur lieu de publication. Une majorité de répondantes et répondants jugent favorablement l'idée de créer un dépôt institutionnel à l'Université Laval, même si quelques personnes indiquent ne pas compren dre clairement quels services seront offerts par le dépôt. Les suggestions des services espérés du dépôt institutionnel ont été nombreuses. Voici les plus demandées : • Assurer une meilleure visibilité des publications sur le Web. • Créer des listes à jour de s publications des chercheuses et chercheurs de l'Université Laval. • Garantir la pérennité des publications. • Intégrer cette base de données avec les outils de gestion de la recherche à l'Université Laval (par exemple le rapport d'activités) ou des services externes comme le CV commun canadien. Environ 10% des répondantes et répondants ont indiqué que ce dépôt leur serait inutile en raison des moyens déjà disponibles de mettre leurs travaux en ligne et en accès libre, tels les réseaux sociaux scientifiques ou les grandes bases de données disciplinaires. D'autres personnes réitèrent leur conviction que les revues scientifiques ne permettront pas d'utiliser un tel dépôt pour diffuser leurs publications.Université Lava

Polarization holography for vortex retarders recording: laboratory demonstration

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

Mid-IR AGPMs for ELT applications

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.Comment: 8 pages, 5 figures, Proc. of SPIE Vol. 9147 (2014

Opal-like photonic structuring of perovskite solar cells using a genetic algorithm approach

Light management is an important area of photovoltaic research, but little is known about it in perovskite solar cells. The present work numerically studies the positive effect of structuring the photo-active layer of perovskite material. This structuration consists of a hybrid absorbing layer made of an uniform part and an opal-like part. A genetic algorithm approach allows us to determine the optimal combination among more than 1.4 10 potential combinations. The optimal combination provides an internal quantum efficiency of 98.1%, nearly 2% higher than for an equivalent unstructured photo-active layer. The robustness of the optimum against potential experimental deviations, as well as the angular dependency of the proposed structure, are examined in the present study.ELSSOL; ARC - Actions de Recherche Concerté

The VORTEX project: first results and perspectives

(abridged) Vortex coronagraphs are among the most promising solutions to perform high contrast imaging at small angular separations. They feature a very small inner working angle, 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 subwavelength 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 $6\times 10^{-5}$ at $2 \lambda/D$. Three of them have now been installed on world-leading diffraction-limited infrared cameras (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 imagers and on future extremely large telescopes (ELTs).Comment: To appear in SPIE proceedings vol. 914

Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4)

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 2{\pi} 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.Comment: 9 page

Epistemic injustices and participatory research: A research agenda at the crossroads of university and community

This article presents an innovative framework to evaluate participatory research. The framework, comprising both a methodology and a self-assessment tool, was developed through a participatory approach to knowledge production and mobilisation. This process took place over the last two years as we, a multidisciplinary team made up of researchers and community-based organisation members from the Groupe de recherche et de formation sur la pauvreté au Québec, were building a scientific program on social injustices and participatory research. We argue that participatory research can help provide a university-community co-constructed response to epistemic injustices embedded within the processes of knowledge production. From our perspective, the mobilisation of knowledge from the university and the community, initiated at the earliest stages of the creation of a research team, is part of a critical approach to the academic production of knowledge. It also constitutes a laboratory for observing, understanding and attempting to reduce epistemic injustices through building bridges between team members. The article focuses on two dimensions of the framework mentioned above: (1) The methodology we established to build co-learning spaces at the crossroads of university and community-based organisations (recruitment of a coordinator to organise and facilitate the workshops, informal and friendly meetings, regular clarification of the process and rules of operation, time for everyone to express themselves, informal preparatory meetings for those who wanted them, financial compensation where required, etc.); and (2) A self-assessment tool available in open access that we built during the process to help academics and their partners engage in a reflexive evaluation of participatory research processes from the point of view of epistemic injustices. Throughout we pay particular attention to challenges inherent in our research program and our responses, and finish with some concluding thoughts on key issues that emerged over the course of two years’ research

Mid-IR AGPMs for ELT applications

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