References of "Lenaerts, Cedric"
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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 detailHigh transmission efficiency for surface plasmon resonance by use of a dielectric grating
Lenaerts, Cedric ULg; Michel, Fabrice ULg; Tilkens, Bernard et al

in Applied Optics (2005), 44(28), 6017-6022

The efficiency of the transmission of surface plasmon waves by use of a dielectric diffraction grating is discussed. The Kretschmann device allows us to obtain a surface plasmon resonance that consists of ... [more ▼]

The efficiency of the transmission of surface plasmon waves by use of a dielectric diffraction grating is discussed. The Kretschmann device allows us to obtain a surface plasmon resonance that consists of an absorption peak in the reflection spectrum. When surface plasmon resonance occurs, the TM-polarization mode of the incident electromagnetic wave is neither transmitted nor reflected. The procedure to transform an absorption peak into a transmission peak is described. Transmittivity of 68% is obtained for a simple structure that consists of a thin-film layer of Ag coated on a volume diffraction grating and embedded between two dielectric media. The results presented herein were obtained by numerical simulations that were carried out by use of an algorithm based on the rigorous coupled-wave theory. [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 detailNarrow band-width wavelength filter by guided mode resonance
Lenaerts, Cedric ULg; Moreau, Vincent; Renotte, Yvon ULg et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2004), 43(11), 2631-2639

Simple resonant structures that permit holographic reflection filtering are studied. The filters under study work under a 45-deg incidence for a wavelength of λ=632.8 nm, a condition useful for future ... [more ▼]

Simple resonant structures that permit holographic reflection filtering are studied. The filters under study work under a 45-deg incidence for a wavelength of λ=632.8 nm, a condition useful for future inclusion in substrate mode systems. First, the influence of the structural parameters of the grating and the waveguide on the position and the shape of the resonance peaks are studied by numerical computation. The numerical results, obtained within the rigorous coupled wave theory, are compared with the measured response of some filters. These filters contain a grating recorded by holography deposited on the substrate. In the case of the bilayer filter, a waveguide is introduced between the grating and the substrate. Second, the numerical results are used for the conception of an active substrate mode spectral filter built from electro-optic zinc oxide. [less ▲]

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See detailBirefringent achromatic phase shifters for nulling interferometry and phase coronagraphy
Mawet, D.; Baudrand, J.; Lenaerts, Cedric ULg et al

in Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (2003, October 01)

Achromatic Phase Shifters are mandatory components in the field of nulling interferometry and phase coronagraphy. Indeed, in order to detect faint objects (e.g. exo-planets) around a central bright star ... [more ▼]

Achromatic Phase Shifters are mandatory components in the field of nulling interferometry and phase coronagraphy. Indeed, in order to detect faint objects (e.g. exo-planets) around a central bright star, one must attenuate the latter by all means. To do this, the most efficient way is to "create" a destructive interference on the blinding light. This technique is called nulling and is common to the two fields mentioned above; the first with several telescopes, the second with only a single aperture. How does it work? The incoming light from the central object is divided into several beams on which one applies a differential Ï phase shift by means of these so-called phase shifters. Then, when the beams are properly recombined together, they simply subtract from each other. "Achromatic" means that we can apply this process over a large spectral bandwidth. This quality will not only be required for the detection and characterization of exo-planets but also for several other astrophysical objects involving huge contrasts like dust shells around young bright stars, AGN,... The proposed birefringent phase shifters and the original implementation schemes we suggest should provide flexible and powerful solutions for these purposes. [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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See detailCustomization of a self-processing polymer for obtaining specific diffractive optical elements
Carre, C.; Saint-Georges, Philippe ULg; Lenaerts, Cedric ULg et al

in Synthetic Metals (2002), 127

Photopolymerizable materials are capable of recording volume holograms via a change in refractivity of the layer. On illumination by an interference pattern around 500 nm, polymerization and diffusion led ... [more ▼]

Photopolymerizable materials are capable of recording volume holograms via a change in refractivity of the layer. On illumination by an interference pattern around 500 nm, polymerization and diffusion led to regions with various segment densities. A modulation of the refractive index took place, thus giving rise to permanent thick phase gratings created in situ in the emulsion. This modulation was estimated at 7 x 10(-3), corresponding to diffraction efficiencies of ca. 80% for transmission holography. Applications for the fabrication of diffractive optical elements can be expected in view of the experimental results and the simplicity of use. For instance, the duplication of computer-generated holograms on a photopolymerizable film led to thick phase holograms with higher diffraction efficiencies. Substrate-mode polarizing elements were also produced, taking advantage of the laminated property since this emulsion was embedded between two glass plates. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailNon-Gaussian electrical fluctuations in a quasi-2d packing of metallic beads
Vandewalle, Nicolas ULg; Lenaerts, Cedric ULg; Dorbolo, Stéphane ULg

in Europhysics Letters [=EPL] (2001), 53(2), 197-201

The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non ... [more ▼]

The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non-Gaussian and seem to belong to Levy stable distributions. Anticorrelations have been also found for the sign of these fluctuations. [less ▲]

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