Coronagraphic phase diversity: performance study and laboratory demonstration

The final performance of current and future instruments dedicated to exoplanet detection and characterization (such as SPHERE on the European Very Large Telescope, GPI on Gemini North, or future instruments on Extremely Large Telescopes) is limited by uncorrected quasi-static aberrations. These aberrations create long-lived speckles in the scientific image plane, which can easily be mistaken for planets. Common adaptive optics systems require dedicated components to perform wave-front analysis. The ultimate wave-front measurement performance is thus limited by the unavoidable differential aberrations between the wavefront sensor and the scientific camera. To reach the level of detectivity required by high-contrast imaging, these differential aberrations must be estimated and compensated for. In this paper, we characterize and experimentally validate a wave-front sensing method that relies on focal-plane data. Our method, called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), is based on a Bayesian approach, and it consists in an extension of phase diversity to high-contrast imaging. It estimates the differential aberrations using only two focal-plane coronagraphic images recorded from the scientific camera itself. In this paper, we first present a thorough characterization of COFFEE's performance by means of numerical simulations. This characterization is then compared with an experimental validation of COFFEE using an in-house adaptive optics bench and an apodized Roddier & Roddier phase mask coronagraph. An excellent match between experimental results and the theoretical study is found. Lastly, we present a preliminary validation of COFFEE's ability to compensate for the aberrations upstream of a coronagraph.Comment: A&A accepte

High-order myopic coronagraphic phase diversity (COFFEE) for wave-front control in high-contrast imaging systems

The estimation and compensation of quasi-static aberrations is mandatory to reach the ultimate performance of high-contrast imaging systems. COFFEE is a focal plane wave-front sensing method that consists in the extension of phase diversity to high-contrast imaging systems. Based on a Bayesian approach, it estimates the quasi-static aberrations from two focal plane images recorded from the scientific camera itself. In this paper, we present COFFEE's extension which allows an estimation of low and high order aberrations with nanometric precision for any coronagraphic device. The performance is evaluated by realistic simulations, performed in the SPHERE instrument framework. We develop a myopic estimation that allows us to take into account an imperfect knowledge on the used diversity phase. Lastly, we evaluate COFFEE's performance in a compensation process, to optimize the contrast on the detector, and show it allows one to reach the 10^-6 contrast required by SPHERE at a few resolution elements from the star. Notably, we present a non-linear energy minimization method which can be used to reach very high contrast levels (better than 10^-7 in a SPHERE-like context)Comment: Accepted in Optics Expres

Comparison of the photoluminescence properties of semiconductor quantum dots and non-blinking diamond nanoparticles. Observation of the diffusion of diamond nanoparticles in living cells

Long-term observations of photoluminescence at the single-molecule level were until recently very diffcult, due to the photobleaching of organic ?uorophore molecules. Although inorganic semiconductor nanocrystals can overcome this diffculty showing very low photobleaching yield, they suffer from photoblinking. A new marker has been recently introduced, relying on diamond nanoparticles containing photoluminescent color centers. In this work we compare the photoluminescence of single quantum dots (QDs) to the one of nanodiamonds containing a single-color center. Contrary to other markers, photoluminescent nanodiamonds present a perfect photostability and no photoblinking. At saturation of their excitation, nanodiamonds photoluminescence intensity is only three times smaller than the one of QDs. Moreover, the bright and stable photoluminescence of nanodiamonds allows wide field observations of single nanoparticles motion. We demonstrate the possibility of recording the tra jectory of such single particle in culture cells

25-nm diamond crystals hosting single NV color centers sorted by photon-correlation near-field microscopy

Diamond nanocrystals containing highly photoluminescent color centers are attractive non-classical and near-field light sources. For near-field applications the size of the nanocrystal is crucial since it defines the optical resolution. NV (Nitrogen-Vacancy) color centers are efficiently created by proton irradiation and annealing of a nanodiamond powder. Using near-field microscopy and photon statistics measurements, we show that nanodiamond with size down to 25 nm can hold a single NV color center with bright and stable photoluminescence

Un dispositif pour favoriser l’engagement des étudiants dans la rédaction de leur rapport de stage

Cet article rapporte la mise en place et l’analyse d’un dispositif qui a pour objectif de soutenir l’engagement des étudiants de master Métiers de l’édition dans l’écriture d’un rapport de stage. L’engagement sera étudié à travers le prisme de l’utilité, du sentiment d’efficacité personnelle et des attentes des étudiants (en termes de réussite). Le dispositif repose sur l’ajout i) d’un atelier sur l’identification et la formulation des compétences et ii) d’un rendu fractionné du rapport au dispositif existant (grille d’évaluation critériée et guide de rédaction). Les résultats suggèrent que l’atelier aide les étudiants à mieux appréhender les objectifs du rapport de stage et soutient leur engagement au travers d’une augmentation de la valeur attribuée à la tâche. Le feedback régulier via l’atelier et le rendu fractionné semblent renforcer le sentiment d’efficacité personnelle en améliorant la compréhension des objectifs du rapport de stage et de l’écriture réflexive. Le dispositif se veut également une ressource pour la suite de la carrière puisque les étudiants s’approprient des outils qui devraient favoriser leur insertion professionnelle

Molecular and Morphological Diversity of Lithothamnion spp. (Hapalidiales, Rhodophyta) from Deepwater Rhodolith Beds in the Northwestern Gulf of Mexico

In the Northwestern Gulf of Mexico (NWGMx), subtidal rhodolith beds offshore Louisiana at 45–80 m depth harbor a diverse community of uncharacterized non-geniculate coralline algae including both biogenic and autogenic rhodoliths and other encrusting taxa. Identifying specimens to their correct genus and species is an ongoing process because many available names remain to be validated by comparison to type specimens. Here, comparative DNA sequencing ( psb A, UPA, and COI) and scanning electron microscopy (SEM) are used to assess the molecular and morphological diversity of the rhodolith-forming specimens belonging to the generic concept of Lithothamnion . Phylogenetic and species delimitation analyses of the newly generated sequences from recently dredged specimens at Ewing and Sackett Banks offshore Louisiana reveal the presence of at least six species of Lithothamnion , whose generic placement is confirmed by SEM images of features considered characteristic for the genus. More broadly, our analyses indicate at least eight Lithothamnion species are found in the Gulf of Mexico. Phylogenetic analyses of single ( psb A and COI) and concatenated markers ( psb A, COI and UPA) show that Lithothamnion is polyphyletic