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Cavalier P.,IPAG | Cavalier P.,CEA Grenoble | Villgier J.-C.,CEA Grenoble | Feautrier P.,IPAG | And 2 more authors.
AIP Advances | Year: 2011

A SWIFTS device (Stationary Wave Integrated Fourier Transform Spectrometer) has been realized with an array of 24 Superconducting Nanowire Single Photon Detectors (SNSPD), on-chip integrated under a Si 3N 4 monomode rib-waveguide interferometer. Colored light around 1.55μm wavelength is introduced through end-fire coupling, producing a counter-propagative stationary interferogram over the 40nm wide, 120nm spaced, 4nm thick epi-NbN nanowire array. Modulations in the source bandwidth have been detected using individual waveguide coupled SNSPDs operating in single photon counting mode, which is a step towards light spectrum reconstruction by inverse Fourier transform of the stationary wave intensity. We report the design, fabrication process and in-situ measurement at 4.2K of light power modulation in the interferometer, obtained with variable laser wavelength. Such micro-SWIFTS configuration with 160nm sampling period over 3.84μm distance allows a spectral bandwidth of 2μm and a wavelength resolution of 170nm. The light interferences direct sampling ability is unique and raises wide interest with several potential applications like fringe-tracking, metrology, cryptography or optical tomography. © 2011 Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.


Vojetta G.,CEA Grenoble | Guellec F.,CEA Grenoble | Mathieu L.,CEA Grenoble | Foubert K.,CEA Grenoble | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Proportional photon detection has been demonstrated using linear mode HgCdTe avalanche photodiodes (APDs) hybridized on a specially designed read-out integrated circuit (ROIC). The ROIC was designed to detect photons at a moderate bandwidth (10 MHz) with a low noise of 10 electrons per characteristics time of the ROIC and to be compatible with large area-small pixel focal plane array (FPA) applications. Proportional photon counting was demonstrated by reproducing the Poisson statics for average photon number states ranging between m=0.8 to 8 photons, at low to moderate avalanche gains M=40-200, using both mid-wave infrared (MWIR) and (short-wave infrared) SWIR HgCdTe APDs. The probability distribution function of the gain was estimated from the analysis of the amplitude of detected residual thermal photons in the MWIR APDs. The corresponding probability distribution functions was characterized by a low excess noise factor F and high asymmetry which favours a high photon detection efficiency (PDE), even at high threshold values. An internal PDE of 90 % was estimated at a threshold level of 40 % of the average signal for a single photon. The dark count rate (DCR) was limited by residual thermal photons in the MWIR APD to about 1 MHz. A geometrical and spectral filtering of this contribution is important to achieve the ultimate performance with MWIR detectors. In this case, the DCR was estimated by interpolation to about 8 kHz. The SWIR HgCdTe APD device had a lower residual photon flux (60 kHz), but was found to be limited by tunnelling dark current noise at high gains at a rate of 100 kHz. © 2012 SPIE.


PubMed | National University of Defense Technology, IPAG, Sun Yat Sen University and Shijiazhuang Mechanical Engineering College
Type: Journal Article | Journal: Medical physics | Year: 2017

In this work, we explore to use very deep convolutional neural network (CNN) for the automatic classification of diabetic retinopathy using color fundus image.We apply translation, stretching, rotation and flipping to the labeled dataset. The original number of labeled-frames is 3000, while after augmentations, 6000 frames with labels are used for the CNN training task. Several different CNN architectures have been proposed and tested. The architecture of our network contains 18 layers with parameters, consists of 12 convolutional layers, some of which followed by max-pooling layers, and two fully connected layers. For a given input, the networks output two probabilities sum to 1, one for each class (as our problem is a two class classification problem).To make a comparison, the performance of CNN-based are compared to previous automatic classification attempts using the hand-crafted features, such as: hard exudates, red lesions, micro-aneurysms and blood vessel detection. We obtained an accuracy of 94.54% on our dataset using CNN, which rank as the highest with the comparison with previous handcrafted features-based classifiers.With limited number of medical staff, an automated system can significantly decrease the tedious manual labor involved in diagnosing large quantities of retinal images. In this work, we explore the potential usage of CNN in retinal image classification. The results are encouraging and a clinical evaluation will be undertaken in order to be able to integrate the presented algorithm in a tool to diagnosis of diabetic retinopathy.


PubMed | National University of Defense Technology, IPAG, Sun Yat Sen University and Shijiazhuang Mechanical Engineering College
Type: Journal Article | Journal: Medical physics | Year: 2017

We explore an automatic anatomical landmarks tracking reset method in the ultrasound liver sequences, with the goal to improve the robustness and accuracy of the tracking.The proposed tracking failure re-initialization method works as follows: before anatomic landmarks tracking is carried out, the image similarity coefficient is calculated (In our method, the complex wavelet structural similarity is used), between the region of interest (ROI) selected in current frame and the ROI in the first frame. If this similarity coefficient exceeds a set threshold, the positions of anatomical landmarks are reset to those which were input for the first frame. This provides a method to prevent accumulation of errors over long sequences, which can lead to erroneous tracking, and amounts to a sort of automatic reset of the tracking starting points based on initial a priori information.The experiments are conducted to track the landmarks in the 5 volunteer B-mode ultrasound liver sequences. The results were evaluated by comparison with manual annotations of liver feature (vessels) throughout each image sequence which were provided after automated tracking was complete. Tracking accuracy was evaluated using the Euclidean distance between tracked points and manually annotated points which was summarized by the mean. The mean error for all ROIs in different sequences are about 1-1.5 mm with the proposed automatic reset method, while the error is about 2 mm without the automatic reset method.Due to the periodic motion of the anatomical landmarks, the proposed image similarity-based automatic re-initialization method can improve the accuracy and robustness of the motion tracking in the ultrasound liver sequences. It may also be applied to other organs tracking problem using ultrasound imaging.


News Article | November 4, 2016
Site: www.eurekalert.org

Rochester Institute of Technology professor Joel Kastner is broadening and deepening his research program on the origins of our solar system and planetary systems orbiting other stars while on four consecutive fellowships and visiting positions during his sabbatical this academic year. Kastner, professor in RIT's Chester F. Carlson Center for Imaging Science and the School of Physics and Astronomy, is the Study Abroad International Faculty Fellow for the month of November at the Arcetri Observatory in Florence, Italy. He is collaborating with former RIT postdoctoral fellow Germano Sacco and other Arcetri scientists to identify and study young stars within a few hundred light years of the sun using newly available data from the European Space Agency's Gaia space telescope. He was also awarded two additional fellowships for 2017--the prestigious Merle A. Tuve Fellowship from the Carnegie Institution for Science Department of Terrestrial Magnetism in Washington, D.C., for his six-week residency there, starting in January 2017; and a Smithsonian Institution Short Term Visitor fellowship for his residency at the Smithsonian Astrophysical Observatory in Cambridge, Mass., in March and April 2017. Prior to his residency in Florence, Kastner spent two months as a visiting astronomer at the Institut de Planetologie et Astronomie de Grenoble, or IPAG, in France, studying the compositions of planet-forming disks around young stars in a collaboration with scientists there who work in the areas of interstellar and solar system chemistry. "The astrophysicists at IPAG, Arcetri, Carnegie and the Smithsonian Astrophysical Observatory are combining observations with the world's most powerful astronomical facilities with sophisticated computer modeling to attack the complex problem of how planetary systems, including our own solar system, have come into being," Kastner said. "I feel very fortunate to be able to work so closely with so many 'black belt' astrophysicists during one sabbatical year."


Kasper M.,ESO | Verinaud C.,IPAG | Mawet D.,ESO Vitacura
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes | Year: 2013

Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based telescopes, the Extremely Large Telescopes, have the potential to dramatically enlarge the discovery space towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. The E-ELT Planetary Camera and Spectrograph (PCS) serves this purpose. Building on the heritage of the EPICS phase-A study, this paper presents revised requirements, a possible concept, and the R&D necessary to realize the instrument.


Costille A.,IPAG | Fusco T.,ONERA
AO for ELT 2011 - 2nd International Conference on Adaptive Optics for Extremely Large Telescopes | Year: 2011

In the frame of the design of instruments for Extremely Large Telescopes, new techniques of Adaptive Optics have been developed. These techniques, generically called Wide Field Adaptive Optics (WFAO), are based on a tomographic reconstruction of the turbulent volume followed by a projection onto Deformable mirrors (DM) in order to ensure a good correction in a specified field of view (FoV). All these systems require a representation of the turbulent volume through the knowledge of the Cn2 profile. It matters both for an accurate simulation of the input perturbations in the case of performance analysis and system design, but also for an efficient model description in the tomographic reconstruction process. We discuss and analyze the impact of the structure and the complexity of the real Cn2 profile onto the WFAO performance. We demonstrate that a classical integrated parameter is not sufficient and that a more complex criterion is mandatory. Then, we focus on the impact of Cn2 model error in the tomographic reconstruction process with respect to the input profile. We demonstrate that number and position of layers are two critical parameters. In conclusion, we show that it is critical to have access to high resolution Cn2 profile to ensure a good performance evaluation of a WFAO system.


Shao M.,Jet Propulsion Laboratory | Nemati B.,Jet Propulsion Laboratory | Zhai C.,Jet Propulsion Laboratory | Goullioud R.,Jet Propulsion Laboratory | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

NEAT, Nearby Exo-Earth Astrometric Telescope is a medium-small telescope ∼ 1m in diameter that is designed to make ultra precise < 1 uas (microarcsec) astrometric measurements of nearby stars in a ∼ 1hr observation. Four major error sources prevent normal space telescopes from obtaining accuracies close to 1 uas. Even with a small 1m telescope, photon noise is usually not a problem for the bright nearby target stars. But in general, the reference stars are much fainter. Typically a field of view of ∼0.5 deg dia is needed to obtain enough bright reference stars. The NEAT concept uses a very simple but unusual design to avoid optically induced astrometric errors. The third source of error is the accuracy and stability of the focal plane. A 1uas error over a ∼2000 arcsec field of view implies the focal plane is accurate or at least stable to 5 parts in 1010 over the lifetime of the mission (∼5yrs). The 4th class of error has to do with our knowledge of the PSF and how that PSF is sampled by an imperfect detector. A Nyquist sampled focal plane would have > 2 pixels per λ/D, and centroiding to 1uas means centroiding to 10-5 pixels. This paper describes the mission concept, and an overview of the technology needed to perform 1uas astrometry with a small telescope, and how we overcome problems 1 and 2. A companion paper will describe the technical progress we've made in solving problems 3 and 4. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).


Arka I.,IPAG | Dubus G.,IPAG
AIP Conference Proceedings | Year: 2012

More than a hundred pulsars have been detected by the Fermi gamma-ray observatory, showing similar spectral characteristics and cutoffs in a narrow range, around a few GeV. The high energy emission is thought to come from outer magnetospheric gaps, however radiation from the equatorial current sheet which separates the two magnetic hemispheres far outside the light cylinder has also been investigated in the past. We discuss the near wind region, defined as the region starting outside the light cylinder (at radius rLC), and spanning to radius r/rLC=R<Γ. Synchrotron radiation from thermal particles in the current sheet in that region can dominate the gamma-ray emission, leading to cutoffs, luminosities and spectra that are similar to the ones observed by the LAT. © 2012 American Institute of Physics.


Costille A.,IPAG | Fusco T.,ONERA
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

New techniques of Adaptive Optics (AO), generically called Wide Field AO, have been developed in the frame of the design study for new instruments for Extremely Large Telescopes (ELT). Concepts such as Multi-Conjugate AO are based on a tomographic reconstruction of the turbulent volume followed by a projection onto DM(s) in order to ensure a good correction in a large Field of View. These systems require a 3D phase reconstruction and a statistical representation of the turbulent volume through the knowledge of the Cn2 profile, which has a strong impact on performance. We focus our study on the analysis of the impact of the structure and the parameters, which define the Cn2 profile, on the performance of a given tomographic system for an ELT. In this article, we perform simulation to emphasize the terms which are directly linked to the knowledge of the true input Cn2 profile, which simulates the input turbulent perturbations, and to the Cn2 profile which is used as a model in the reconstruction process. We determine and discuss the level of the accuracy needed on the Cn2 profile to limit the tomographic error term and to ensure a good performance. We show that a good sampling of the input turbulence is required to ensure performance of the system. © 2012 SPIE.

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