MTF measurements of a type-II superlattice infrared focal plane array sealed in a cryocooler

International audienceIn operational electro-optical systems, infrared focal plane arrays (IR FPA) are integrated in cryocoolers which induce vibrations that may strongly affect their modulation transfer function (MTF). In this paper, we present the MTF measurement of an IR FPA sealed in its cryocooler. The method we use to measure the MTF decorrelates operational constraints and the technological limitations of the IR FPA. The bench is based on the diffraction properties of a continuously self imaging grating (CSIG). The 26 µm pixel size extracted from the MTF measurement is in good agreement with the expected value

Organellar inheritance in the green lineage: insights from Ostreococcus tauri

Along the green lineage (Chlorophyta and Streptophyta), mitochondria and chloroplast are mainly uniparentally transmitted and their evolution is thus clonal. The mode of organellar inheritance in their ancestor is less certain. The inability to make clear phylogenetic inference is partly due to a lack of information for deep branching organisms in this lineage. Here, we investigate organellar evolution in the early branching green alga Ostreococcus tauri using population genomics data from the complete mitochondrial and chloroplast genomes. The haplotype structure is consistent with clonal evolution in mitochondria, while we find evidence for recombination in the chloroplast genome. The number of recombination events in the genealogy of the chloroplast suggests that recombination, and thus biparental inheritance, is not rare. Consistent with the evidence of recombination, we find that the ratio of the number of nonsynonymous to the synonymous polymorphisms per site is lower in chloroplast than in the mitochondria genome. We also find evidence for the segregation of two selfish genetic elements in the chloroplast. These results shed light on the role of recombination and the evolutionary history of organellar inheritance in the green lineage

Life-Cycle and Genome of OtV5, a Large DNA Virus of the Pelagic Marine Unicellular Green Alga Ostreococcus tauri

Large DNA viruses are ubiquitous, infecting diverse organisms ranging from algae to man, and have probably evolved from an ancient common ancestor. In aquatic environments, such algal viruses control blooms and shape the evolution of biodiversity in phytoplankton, but little is known about their biological functions. We show that Ostreococcus tauri, the smallest known marine photosynthetic eukaryote, whose genome is completely characterized, is a host for large DNA viruses, and present an analysis of the life-cycle and 186,234 bp long linear genome of OtV5. OtV5 is a lytic phycodnavirus which unexpectedly does not degrade its host chromosomes before the host cell bursts. Analysis of its complete genome sequence confirmed that it lacks expected site-specific endonucleases, and revealed the presence of 16 genes whose predicted functions are novel to this group of viruses. OtV5 carries at least one predicted gene whose protein closely resembles its host counterpart and several other host-like sequences, suggesting that horizontal gene transfers between host and viral genomes may occur frequently on an evolutionary scale. Fifty seven percent of the 268 predicted proteins present no similarities with any known protein in Genbank, underlining the wealth of undiscovered biological diversity present in oceanic viruses, which are estimated to harbour 200Mt of carbon

Development of a Cryogenic Test Bench for Spectral MTF Measurement on Midwave Infrared Focal Plane Arrays

International audienceThe modulation transfer function (MTF) is one of the key figures of merit for the characterization of infrared focal plane arrays (FPA). Moreover, with both the trend of reduced pixel pitch and the variety of pixel structures observed in the industry, the study of the impact of wavelength on the MTF is also of great interest, and thus needs a spectro-spatial measurement. In this paper, we demonstrate such spectral MTF measurements in the mid-wavelength infrared (MWIR) band by the use of several spectral bandpass filters. We realize those measurements at 80 K on a specific n/p 320 × 256 HgCdTe MWIR FPA, divided into different areas. The pixel pitch is the same for all areas (30 μm), the only difference being the fill factor, which differs from one zone to another. The MTF measurement bench is based on a continuously self-imaging grating interferometer integrated in a specific cryogenic set-up

Caractérisation absolue de la fonction de transfert optique d'un objectif cryogénique infrarouge de grande ouverture

International audienceThe field of infrared detectors is experiencing a strong movement towards smaller pixel pitches, and it is now common to see pitches close to the wavelength. This raises major problems in measuring their characteristics, especially their transfer function. The latter can be measured by optical pattern projection methods using a low F/# objective, such as the spot scan method. However, in order to obtain the quantitative transfer function measurement of detectors, the objective spatial response should be measured and deconvoluted precisely, since the size of the focused optical spot is close to the pixel pitch. Therefore, the purpose of this paper is to propose a protocol that performs an absolute measurement of a high-quality infrared objective. The main idea of the article is to link the measurement standard to a fundamental theory, the Huygens-Fresnel principle, using a particular wavefront sensor as a secondary measurement standard. This has various metrological advantages, that allow the uncertainties of the optical transfer function measurement to be controlled and evaluated. The protocol and the propagation of errors described in the article are both used to demonstrate the value of this approach.Le domaine des détecteurs infrarouges connaît une tendance vers des pas pixels plus petits, et il est désormais courant de voir des pas proches de la longueur d'onde. Ceci pose des problèmes importants pour la mesure de leurs caractéristiques, notamment de leur fonction de transfert. Cette dernière peut être mesurée par des méthodes de projection de motifs optiques utilisant un objectif à faible F/#, comme la méthode du spot scan, mais cela suppose que la réponse spatiale de l'objectif soit mesurée et déconvoluée avec précision, étant donné que la taille de la tache optique focalisée est proche du pas du pixel. L'objectif de cet article est donc de proposer un protocole permettant d'effectuer une mesure absolue d'un objectif infrarouge de haute qualité. L'idée principale de l'article est de relier l'étalon de mesure à une théorie fondamentale, à savoir le principe de Huygens-Fresnel, en utilisant un trou de diffraction couplé à un capteur de front d'onde permettant de restituer les erreurs de mesures

Développement d'un banc de spot scan cryogénique pour l'étude des détecteurs dans le moyen infrarouge

International audienceIn this article, we present a cryogenic spot scan bench in the 3-5 µm band currently under development in the ONERA MIRCOS platform. Initial tests have been carried out on a HgCdTe detector with a 30 µm pitch and improvements are underway to characterise smaller pixels.Dans cet article, nous présentons un banc de spot scan cryogénique dans la bande 3-5 µm actuellement en développement dans la plateforme MIRCOS de l'ONERA. Des premiers tests ont été réalisés sur un détecteur HgCdTe au pas de 30 µm et des améliorations sont en cours pour pouvoir caractériser de plus petits pixels

Caractérisation optique d'un objectif de spot scan cryogénique à faible nombre d'ouverture pour détecteurs infrarouges

International audienceInfrared focal plane arrays are widely used for astronomical observations and are constantly optimized to provide higher-quality images. The knowledge of the pixel spatial response becomes critical to extract ever more data from scientific missions. A specific cryogenic spot scan objective with an f-number of 1.2 has been developed in order to finely characterize 15 µm (or smaller) pixel pitch cooled infrared focal plane arrays in the spectral band between 3-5 µm. It will be operated in the MIRCOS test bench with different narrow-band filters. We present the first optical characterization of this objective obtained with a cryogenic wavefront analyzer-a quadrilateral shearing interferometer. The measured wavefront indicates a peak-to-valley amplitude of 2 µm, which corresponds to an optical quality of about λ/2 at 3.75 µm working wavelength. This value higher than expected might be due to a non-uniform cooling of the objective.Les détecteurs infrarouges sont largement utilisées pour les observations astronomiques et sont constamment optimisées pour fournir des images de meilleure qualité. La connaissance de la réponse spatiale des pixels devient primordiale pour extraire toujours plus de données provenant des missions scientifiques. Un objectif spot scan cryogénique spécifique avec un nombre d'ouverture de 1,2 a été développé afin de caractériser finement les détecteurs infrarouges refroidies avec un pas de 15 μm (ou moins) dans la bande spectrale entre 3-5 μm. Elle sera exploitée dans le banc d'essai MIRCOS avec différents filtres à bande étroite. Nous présentons la première caractérisation optique de cet objectif obtenue avec un analyseur de front d'onde cryogénique - un interféromètre à décalage quadrilatéral. Le front d'onde mesuré indique une amplitude peak-to-valley de 2 μm, ce qui correspond à une qualité optique d'environ λ/2 à une longueur d'onde de travail de 3,75 μm. Cette valeur supérieure à celle attendue pourrait être due à un refroidissement non uniforme de l'objectif

Développement du banc de spot scan cryogénique pour l'étude de détecteurs dans le moyen infrarouge

International audienceIn this article, we present a cryogenic spot scan bench dedicated to the 3-5.5 µm spectral band currently under development in the MIRCOS platform at ONERA. Initial tests have been carried out on a 30 µm pitch HgCdTe focal plane array, and improvements are underway to characterize the spatial response of detectors with smaller pixel pitches.Dans cet article, nous présentons un banc de spot scan cryogénique dédié à la bande spectrale 3-5,5 μm actuellement en cours de développement sur la plateforme MIRCOS de l'ONERA. Les premiers tests ont été réalisés sur un détecteur HgCdTe avec un pas pixel de 30 μm, et des améliorations sont en cours pour caractériser la réponse spatiale de détecteurs avec des pas de pixels plus petits