13,406 research outputs found

    The calibration of interferometric visibilities obtained with single-mode optical interferometers. Computation of error bars and correlations

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    I present in this paper a method to calibrate data obtained from optical and infrared interferometers. I show that correlated noises and errors need to be taken into account for a very good estimate of individual error bars but also when model fitting the data to derive meaningful model parameters whose accuracies are not overestimated. It is also shown that under conditions of high correlated noise, faint structures of the source can be detected. This point is important to define strategies of calibration for difficult programs such as exoplanet detection. The limits of validity of the assumptions on the noise statistics are discussed

    Anderson v. State: The Consent to Search Doctrine Revisited

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    Subtracting the photon noise bias from single-mode optical interferometer visibilities

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    I present in this paper a method to subtract the bias due to source photon noise from visibilities measured with a single-mode optical interferometer. Properties of the processed noise are demonstrated and examples of subtraction on real data are presented.Comment: To appear in Astronomy & Astrophysic

    Pupil remapping for high contrast astronomy: results from an optical testbed

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    The direct imaging and characterization of Earth-like planets is among the most sought-after prizes in contemporary astrophysics, however current optical instrumentation delivers insufficient dynamic range to overcome the vast contrast differential between the planet and its host star. New opportunities are offered by coherent single mode fibers, whose technological development has been motivated by the needs of the telecom industry in the near infrared. This paper presents a new vision for an instrument using coherent waveguides to remap the pupil geometry of the telescope. It would (i) inject the full pupil of the telescope into an array of single mode fibers, (ii) rearrange the pupil so fringes can be accurately measured, and (iii) permit image reconstruction so that atmospheric blurring can be totally removed. Here we present a laboratory experiment whose goal was to validate the theoretical concepts underpinning our proposed method. We successfully confirmed that we can retrieve the image of a simulated astrophysical object (in this case a binary star) though a pupil remapping instrument using single mode fibers.Comment: Accepted in Optics Expres

    High dynamic range imaging with a single-mode pupil remapping system : a self-calibration algorithm for redundant interferometric arrays

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    The correction of the influence of phase corrugation in the pupil plane is a fundamental issue in achieving high dynamic range imaging. In this paper, we investigate an instrumental setup which consists in applying interferometric techniques on a single telescope, by filtering and dividing the pupil with an array of single-mode fibers. We developed a new algorithm, which makes use of the fact that we have a redundant interferometric array, to completely disentangle the astronomical object from the atmospheric perturbations (phase and scintillation). This self-calibrating algorithm can also be applied to any - diluted or not - redundant interferometric setup. On an 8 meter telescope observing at a wavelength of 630 nm, our simulations show that a single mode pupil remapping system could achieve, at a few resolution elements from the central star, a raw dynamic range up to 10^6; depending on the brightness of the source. The self calibration algorithm proved to be very efficient, allowing image reconstruction of faint sources (mag = 15) even though the signal-to-noise ratio of individual spatial frequencies are of the order of 0.1. We finally note that the instrument could be more sensitive by combining this setup with an adaptive optics system. The dynamic range would however be limited by the noise of the small, high frequency, displacements of the deformable mirror.Comment: 11 pages, 7 figures. Accepted for publication in MNRA

    Functional Methods and Effective Potentials for Nonlinear Composites

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    A formulation of variational principles in terms of functional integrals is proposed for any type of local plastic potentials. The minimization problem is reduced to the computation of a path integral. This integral can be used as a starting point for different approximations. As a first application, it is shown how to compute to second-order the weak-disorder perturbative expansion of the effective potentials in random composite. The three-dimensional results of Suquet and Ponte-Casta\~neda (1993) for the plastic dissipation potential with uniform applied tractions are retrieved and extended to any space dimension, taking correlations into account. In addition, the viscoplastic potential is also computed for uniform strain rates.Comment: 20 pages, accepted for publication in JMP

    Updated results on prototype chalcogenide fibers for 10-um wavefront spatial filtering

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    The detection of terrestrial planets by Darwin/TPF missions will require extremely high quality wavefronts. Single-mode fibers have proven to be powerful beam cleaning components in the near-infrared, but are currently not available in the mid-infrared where they would be critically needed for Darwin/TPF. In this paper, we present updated measurements on the prototype chalcogenide fibers we are developing for the purpose of mid-infrared spatial filtering. We demonstrate the guiding property of our 3rd generation component and we characterize its filtering performances on a 4 mm length: the far-field radiation pattern matches a Gaussian profile at the level of 3% rms and 13% pk-pk.Comment: 4 pages, 5 figures, to appear in the proceedings of the conference "Toward Other Earths, Darwin/TPF and the search for extrasolar terrestrial planets", held in Heidelberg, Germany, 22-25 April 2003, ESA SP-53

    Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in diamond anvil cell. Application to the stability study of AlPdMn

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    We report an innovative high pressure method combining the diamond anvil cell device with the technique of picosecond ultrasonics. Such an approach allows to accurately measure sound velocity and attenuation of solids and liquids under pressure of tens of GPa, overcoming all the drawbacks of traditional techniques. The power of this new experimental technique is demonstrated in studies of lattice dynamics, stability domain and relaxation process in a metallic sample, a perfect single-grain AlPdMn quasicrystal, and rare gas, neon and argon. Application to the study of defect-induced lattice stability in AlPdMn up to 30 GPa is proposed. The present work has potential for application in areas ranging from fundamental problems in physics of solid and liquid state, which in turn could be beneficial for various other scientific fields as Earth and planetary science or material research
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