References of "Mawet, Dimitri"
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See detailScience case for 1 mas spectro-imagining in the near-infrared
Garcia, Paulo J V; Berger, Jean-Phillipe; Marconi, Alessandro et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

We present the work developed within the science team of the Very Large Telescope Interferometer Spectro-Imager (VSI) during the Phase A studies. VSI aims at delivering ~ 1 milliarcsecond resolution data ... [more ▼]

We present the work developed within the science team of the Very Large Telescope Interferometer Spectro-Imager (VSI) during the Phase A studies. VSI aims at delivering ~ 1 milliarcsecond resolution data cubes in the near-infrared, with several spectral resolutions up to 12 000, by combining up to 8 VLTI telescopes. In the design of an instrument, the science case plays a central role by supporting the instrument construction decision, defining the top-level requirements and balancing design options. The overall science philosophy of VSI was that of a general user instrument serving a broad community. The science team addressed themes which included several areas of astrophysics and illustrated specific modes of operation of the instrument: a) YSO disks and winds; b) Multiplicity of young stars; c) Exoplanets; d) Debris disks; e) Stellar surface imaging; f) The environments of evolved stars; g) AGN tori; h) AGN's Broad Line Region; i) Supermassive black-holes; and j) Microlensing. The main conclusions can be summarized as follows: a) The accessible targets and related science are extremely sensitive to the instrument limiting magnitude; the instrument should be optimized for sensitivity and have its own fringe tracker. b) Most of the science cases are readily achievable with on-axis fringe tracking, off-axis fringe tracking enabling extra science. c) In most targets (YSOs, evolved stars and AGNs), the interpretation and analysis of circumstellar/nuclear dust morphology requires direct access to the gas via spectral resolved studies of emission lines, requiring at least a spectral resolution of 2 500. d) To routinely deliver images at the required sensitivity, the number of telescopes in determinant, with 6 telescopes being favored. e) The factorial increase in the number of closure phases and visibilities, gained in a single observation, makes massive surveys of parameters and related science for the first time possible. f) High dynamic range imaging and very high dynamic range differential closure phase are possible allowing the study of debris disks and characterization of pegasides. g) Spectro-imaging in the near-infrared is highly complementary to ALMA, adaptive optics and interferometric imaging in the thermal infrared. [less ▲]

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See detailThe development and applications of a ground-based fiber nulling coronagraph
Martin, Stefan; Serabyn, Eugene; Liewer, Kurt et al

in Optical and Infrared Interferometry (2008, July)

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See detailInfrared achromatic phase shifters using modulated total internal reflection
Mawet, Dimitri; Lenaerts, Cédric; Riaud, Pierre ULg et al

in Monnier, John D; Schöller, Markus; Danchi, William C (Eds.) Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series "Advances in Stellar Interferometry" - SPIE Conference 6268 (2006, July 01)

We propose a new family of achromatic phase shifters that uses the modulated total internal reflection (TIR) phenomenon. These components can be seen as enhanced Fresnel rhombs for infrared applications ... [more ▼]

We propose a new family of achromatic phase shifters that uses the modulated total internal reflection (TIR) phenomenon. These components can be seen as enhanced Fresnel rhombs for infrared applications like nulling interferometry and polarimetry. The TIR phenomenon comes with a differential phase shift between the polarization components of the incident light. Modulating the index transition at the TIR interface allows compensating for the intrinsic material dispersion in order to make the subsequent phase shift achromatic over broad bands. The modulation can be induced by a thin film of a well-chosen medium or a subwavelength grating whose parameters are specially optimized. We present results from theoretical simulations together with preliminary fabrication outcomes. [less ▲]

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See detailNew generation phase coronagraphy
Mawet, Dimitri; Riaud, Pierre; Baudrand, Jacques et al

Poster (2006)

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See detailAntireflective subwavelength patterning of IR optics
Vandormael, Denis; Habraken, Serge ULg; Loicq, Jerôme ULg et al

in Proceedings of SPIE (2006), 6395

Thermal infrared (IR) lenses require efficient anti-reflection coating. Moth-eye (or egg-box) 2D subwavelength gratings have demonstrated their ability to reach a very high transmission for a wide ... [more ▼]

Thermal infrared (IR) lenses require efficient anti-reflection coating. Moth-eye (or egg-box) 2D subwavelength gratings have demonstrated their ability to reach a very high transmission for a wide wavelength and angular range. The use in thermal IR is simplified by the lower resolution for lithographic technology, compared to visible waveband. However, deeper structures must be engraved and lithography must be adapted to IR materials. In order to be cost-effective, the patterning must be produced by replication techniques, such as embossing. Our laboratory is now experimenting hot embossing of moth-eye patterns in chalcogenide substrates. In this paper, theoretical analysis, micro-lithographic technology and manufacturing processes are detailed. [less ▲]

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See detailSubwavelength surface-relief gratings for stellar coronagraphy
Mawet, Dimitri; Riaud, Pierre ULg; Surdej, Jean ULg et al

in Applied Optics (2005), 44 Issue 34

We present a new design of a phase mask coronagraph implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. Phase mask coronagraphy is a recent ... [more ▼]

We present a new design of a phase mask coronagraph implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. Phase mask coronagraphy is a recent technique that seeks to accommodate both high dynamic and high angular resolution imaging of faint sources around bright astrophysical objects such as exoplanets orbiting their host stars. The original design we propose is a new, integrated, and flexible solution to the pi phase-shift chromaticity of the phase mask coronagraphs. It will allow broadband observations, i.e., shorter integration times and object characterizations, by means of spectroscopic analysis. The feasibility of the component manufacturing is also considered through a tolerance study. [less ▲]

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See detailUse of subwavelength gratings in TIR incidence as achromatic phase shifters
Mawet, Dimitri; Lenaerts, Cedric ULg; Riaud, Pierre ULg et al

in Optics Express (2005), 13(22), 8686-8692

Nulling interferometry constitutes a very promising technique in observational astrophysics. This method consists in attenuating the signal of a bright astrophysical object in order to detect much fainter ... [more ▼]

Nulling interferometry constitutes a very promising technique in observational astrophysics. This method consists in attenuating the signal of a bright astrophysical object in order to detect much fainter nearby features, e.g. exoplanets around their host star. An on-axis destructive interference is created by adjusting the phases of the beams coming from various telescopes. The huge flux ratio between the parent star and the planet (106 in the thermal infrared) requires unprecedented high performance broadband phase shifters. We present a new design for these key components called Achromatic Phase Shifters (APS). We propose to use subwavelength diffractive optical elements under total internal reflection (TIR) incidence. Our component can be seen as an evolution of the Fresnel Rhomb technology. [less ▲]

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See detailThe four-quadrant ZOG and annular groove phase mask coronagraphs
Mawet, Dimitri; Riaud, Pierre ULg; Absil, Olivier ULg et al

in Coulter, Daniel R (Ed.) Techniques and Instrumentation for Detection of Exoplanets II (2005, August 01)

Phase mask coronagraphy is a technique aiming at accommodating both high dynamic and high angular resolution imaging of faint sources around bright objects such as exo-planets orbiting their parent stars ... [more ▼]

Phase mask coronagraphy is a technique aiming at accommodating both high dynamic and high angular resolution imaging of faint sources around bright objects such as exo-planets orbiting their parent stars or host galaxies around Active Galactic Nuclei. We present two new phase mask coronagraphs implemented with subwavelength diffractive optical elements consisting of optimized surface-relief gratings. The first one is an evolution of the Four Quadrant Phase Mask coronagraph, which resolves the Ï phase shift chromaticity problem: the Four Quadrant Zeroth Order Grating (4QZOG). The second one is a totally new design consisting of an optical vortex induced by a space-variant grating: the Annular Groove Phase Mask (AGPM) coronagraph is fully symmetric and free from any "shaded zones". Some manufacturing hints are given. [less ▲]

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See detailLimitation of the Pupil Replication Technique in the Presence of Instrumental Defects
Riaud, Pierre ULg; Mawet, Dimitri; Absil, Olivier ULg

in Astrophysical Journal Letters (2005), 628

Pupil replication has been proposed by Greenaway et al. as a new optical technique to improve the suppression of starlight in high dynamic imaging. This Letter extends numerical simulations in the two ... [more ▼]

Pupil replication has been proposed by Greenaway et al. as a new optical technique to improve the suppression of starlight in high dynamic imaging. This Letter extends numerical simulations in the two-dimensional case with various realistic imperfections (surface error, chromatic smearing, and pupil shift). These results demonstrate some strong limitations compared to single-pupil apodization techniques for exoplanet detection. [less ▲]

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See detailPerspectives for next generation ground- and space-based interferometers (plenary session, invited)
Absil, Olivier ULg; Mawet, Dimitri

Scientific conference (2005, July 07)

The advent of large interferometric facilities such as the VLTI has recently offered the opportunity to the astronomical community to study various targets with an unprecedented angular resolution in the ... [more ▼]

The advent of large interferometric facilities such as the VLTI has recently offered the opportunity to the astronomical community to study various targets with an unprecedented angular resolution in the near- and mid-infrared. In this talk, we shortly review the main scientific topics that have largely benefited from interferometric studies in the past years, and present the future scientific challenges for interferometry. Some of these challenges will already be (partially) within reach when the second generation of VLTI instrumentation comes online, but most of them require more ambitious facilities to be built in the future. In this review talk, we recall the basic concepts of optical/IR interferometry and present some perspectives for future ground- and space-based interferometric facilities. Both approaches lead to major technological challenges that need to be overcome in the next decade. [less ▲]

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See detailAchromatic four quadrants phase mask coronagraph using the dispersion of form birefringence
Mawet, Dimitri; Lenaerts, Cedric ULg; Moreau, Vincent et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2003, February 01)

We describe an alternative design for the 4-quadrant phase mask coronagraph described recently by Rouan et al. 2000. Based on the same principle, i.e. producing a very efficient nulling by mutually ... [more ▼]

We describe an alternative design for the 4-quadrant phase mask coronagraph described recently by Rouan et al. 2000. Based on the same principle, i.e. producing a very efficient nulling by mutually destructive interferences of the coherent light from the main source, our mask realises the pi phase shift using some properties of ZOGs (Zeroth Order Gratings) and according to an original scheme respecting the 4-quadrant symmetry. When the period of the one-dimension grating structure is smaller than the wavelength of the incident light, the structure becomes birefringent. The effective refractive indices depend on the wavelength. Using this feature, we can design a mask whose nulling e±ciency is maintained within a wide wavelength range. Numerical simulations were made according to the RCWT (Rigorous Coupled Wave Theory). [less ▲]

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