Dr. Laurent Koechlin Profile

Dr. Laurent Koechlin

at Observatoire Midi-Pyrénées

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Publications (13)

Proceedings Article | 21 November 2017 Open Access

Astrophysical targets of the Fresnel diffractive imager

L. Koechlin, P. Deba, T. Raksasataya

Proceedings Volume 10566, 1056602 (2017) https://doi.org/10.1117/12.2308243

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The Fresnel Diffractive imager is an innovative concept of distributed space telescope, for high resolution (milli arc-seconds) spectro-imaging in the IR, visible and UV domains. This paper presents its optical principle and the science that can be done on potential astrophysical targets.

The novelty lies in the primary optics: a binary Fresnel array, akin to a binary Fresnel zone plate. The main interest of this approach is the relaxed manufacturing and positioning constraints. While having the resolution and imaging capabilities of lens or mirrors of equivalent size, no optical material is involved in the focusing process: just vacuum. A Fresnel array consists of millions void subapertures punched into a large and thin opaque membrane, that focus light by diffraction into a compact and highly contrasted image. The positioning law of the aperture edges drives the image quality and contrast.

This optical concept allows larger and lighter apertures than solid state optics, aiming to high angular resolution and high dynamic range imaging, in particular for UV applications. Diffraction focusing implies very long focal distances, up to dozens of kilometers, which requires at least a two-vessel formation flying in space.

The first spacecraft, “the Fresnel Array spacecraft”, holds the large punched foil: the Fresnel Array. The second, the “Receiver spacecraft” holds the field optics and focal instrumentation. A chromatism correction feature enables moderately large (20%) relative wavebands, and fields of a few to a dozen arc seconds.

This Fresnel imager is adapted to high contrast stellar environments: dust disks, close companions and (we hope) exoplanets. Specific to the particular grid-like pattern of the primary focusing zone plate, is the very high dynamic range achieved in the images, in the case of compact objects.

Large stellar photospheres may also be mapped with Fresnel arrays of a few meters opertaing in the UV. Larger and more complex fields can be imaged with a lesser dynamic range: galactic or extragalactic, or at the opposite distance scale: small solar system bodies. This paper will briefly address the optical principle, and in more detail the astrophysical missions and targets proposed for a 4-meter class demonstrator:

– Exoplanet imaging, Exoplanet spectroscopic analysis in the visible and UV,

– Stellar environments, young stellar systems, disks,

– Galactic clouds, astrochemistry,

– IR observation of the galactic center,

– Small objects of our solar system.

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Proceedings Article | 11 July 2016 Paper

An optimized Fresnel array for a test space mission in UV

W. Roux, L. Koechlin

Proceedings Volume 9905, 99053E (2016) https://doi.org/10.1117/12.2232100

KEYWORDS: Ultraviolet radiation, Point spread functions, Ultraviolet radiation, Sensors, Microchannel plates, Amplifiers, Electronics, Field programmable gate arrays, Analog electronics, Connectors, Space telescopes

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The Fresnel Diffractive Imager is based on a new optical concept for space telescopes, developed at Institut de Recherche en Astrophysique et Planétologie (IRAP) in Toulouse, France. We propose it for space missions dedicated to science cases in the Ultra-Violet with aperture ranges from 6 to 30 meters. Instead of a classical mirror to focus light, this concept uses very light-weight diffractive optics : the Fresnel array. Our project has already proved its performances in terms of resolution and high dynamic range in the laboratory, in the visible and near IR. It has been tested successfully on real astrophysical sources from the ground.

At present, the project has reached the stage where a probatory mission is needed to validate its operation in space. In collaboration with institutes in Spain and Russia, we will propose a mission to the Russian space agency Roscosmos, to board a small prototype Fresnel imager on the International Space Station (ISS) for a UV astronomy program.

We have improved the Fresnel array design to get a better Point Spread Function (PSF), 2 different ways. Numerical simulations have first allowed us to confirm these optical improvements, before manufacturing the diffractive optics and using them for new lab tests.

In our previous setups, the opaque Fresnel zones in the primary Fresnel array (playing the role of the telescope objective) were maintained with an orthogonal bars mesh, following the pseudo-period of the Fresnel zones. We show that the PSF improves when these bars are regularly spaced. Furthermore, the optical system is apodized to get a better peaked PSF, and increase its high contrast performances.

In our case, to apodize a binary mask the solution is to modulate the Fresnel zones in relative thickness ratio (opaque versus void), thus driving the local light transmission ratio. In earlier implementations, our Fresnel arrays were apodized with a circularly symmetric law, but an orthogonal apodization law is more efficient. That is why we are developing this particular type of apodized square aperture Fresnel arrays.

Proceedings Article | 29 July 2010 Paper

Fresnel diffractive imager: instrument for space mission in the visible and UV

T. Raksasataya, P. Deba, J. P. Rivet, R. Gili, D. Serre, L. Koechlin

Proceedings Volume 7732, 77322D (2010) https://doi.org/10.1117/12.857213

KEYWORDS: Imaging systems, Ultraviolet radiation, Prototyping, Space operations, Diffraction, Spatial resolution, Visible radiation, Space telescopes, UV optics, Infrared imaging

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Proceedings Article | 20 September 2007 Paper

Fresnel interferometric arrays for space-based imaging: testbed results

Denis Serre, Laurent Koechlin, Paul Deba

Proceedings Volume 6687, 66870I (2007) https://doi.org/10.1117/12.732334

KEYWORDS: Interferometry, Imaging arrays, Diffraction, Point spread functions, Optics manufacturing, Optical components, Colorimetry, Spatial resolution, Zone plates

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Proceedings Article | 20 October 2004 Paper

Field-resolution ratio progresses for interferometric arrays

Laurent Koechlin, Denis Serre, Paul Duchon

Proceedings Volume 5491, (2004) https://doi.org/10.1117/12.551234

KEYWORDS: Interferometry, Wavefronts, Point spread functions, Diffraction, Interferometers, Zone plates, Optical components, Synthetic apertures, Spatial resolution, Mirrors

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Proceedings Article | 26 February 2003 Paper

Hypertelescope imaging: from exoplanets to neutron stars

Antoine Labeyrie, Herve Le Coroller, Julien Dejonghe, Frantz Martinache, Virginie Borkowski, Olivier Lardiere, Laurent Koechlin

Proceedings Volume 4852, (2003) https://doi.org/10.1117/12.460844

KEYWORDS: Stars, Mirrors, Coronagraphy, Space telescopes, Telescopes, Planets, Radio optics, Spherical lenses, Adaptive optics, Diffraction

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Proceedings Article | 21 February 2003 Paper

High angular resolution in 2010-2020: a comparison between possible post-VLT/VLTI instruments

Luc Arnold, Anne-Marie Lagrange, Denis Mourard, Pierre Riaud, Marc Ferrari, Sophie Gillet, Pierre Kern, Laurent Koechlin, Antoine Labeyrie, Olivier Lardiere, Fabien Malbet, Guy Perrin, Gerard Rousset, Michel Tallon

Proceedings Volume 4838, (2003) https://doi.org/10.1117/12.458939

KEYWORDS: Space telescopes, Adaptive optics, Telescopes, Interferometry, Spatial resolution, Interferometers, Point spread functions, Aerospace engineering, Imaging arrays, Synthetic apertures

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Proceedings Article | 21 February 2003 Paper

Limit in field-resolution ratio for interferometric arrays

Laurent Koechlin, Jose-Philippe Perez

Proceedings Volume 4838, (2003) https://doi.org/10.1117/12.459384

KEYWORDS: Interferometry, Visibility, Image processing, Image restoration, Image resolution, Interferometers, Interference (communication), Synthetic apertures, Radio optics, Visible radiation

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Proceedings Article | 5 July 2000 Paper

GI2T/REGAIN control system and data reduction package

Denis Mourard, Jean Clausse, Ettore Pedretti, Monique Pierron, Robert Dalla, Michel Dugue, Laurent Koechlin, Guy Merlin, Nathalie Thureau

Proceedings Volume 4006, (2000) https://doi.org/10.1117/12.390251

KEYWORDS: Control systems, Calibration, Data acquisition, Spectrographs, Detection and tracking algorithms, Interferometers, Distortion, Visibility, Stars, Telecommunications

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Proceedings Article | 24 July 1998 Paper

DELTA photon-counting camera: concept and current status

Sebastien Morel, Laurent Koechlin

Proceedings Volume 3350, (1998) https://doi.org/10.1117/12.317201

KEYWORDS: Photon counting, Cameras, Sensors, Charge-coupled devices, Image intensifiers, Ions, Geometrical optics, Temporal resolution, Interferometry, Atmospheric turbulence

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Proceedings Article | 24 July 1998 Paper

Fringe tracking using a priori information on the optical path difference drift

Sebastien Morel, Laurent Koechlin

Proceedings Volume 3350, (1998) https://doi.org/10.1117/12.317174

KEYWORDS: Autoregressive models, Fringe analysis, Signal to noise ratio, Optical tracking, Detection and tracking algorithms, Fourier transforms, Visibility, Atmospheric turbulence, Interferometers, Photon counting

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Proceedings Article | 13 September 1994 Paper

Concept of field-to-resolution ratio in aperture synthesis

Andre Lannes, Eric Anterrieu, Laurent Koechlin, Geraldine Fitoussi

Proceedings Volume 2209, (1994) https://doi.org/10.1117/12.185273

KEYWORDS: Error analysis, Fourier transforms, Synthetic apertures, Interferometry, Deconvolution, Cerium, Condition numbers, Astronomy, Lutetium, Convolution

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Proceedings Article | 1 July 1990 Open Access

VLT interferometer: proposed implementation

Jacques Beckers, Daniel Enard, Michel Faucherre, Fritz Merkle, G. Di Benedetto, R. Braun, R. Foy, Reinhard Genzel, Laurent Koechlin, Gerd Weigelt

Proceedings Volume 1236, (1990) https://doi.org/10.1117/12.19191

KEYWORDS: Telescopes, Interferometry, Interferometers, Mirrors, Adaptive optics, Optical telescopes, Fermium, Frequency modulation, Infrared telescopes, Relays

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