Showing results 21 to 23 of 23
  Achromatic four quadrants phase mask coronagraph using the dispersion of form birefringence; Lenaerts, Cedric  ; et alin 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 ▲] Detailed reference viewed: 14 (5 ULg) Customization of a self-processing polymer for obtaining specific diffractive optical elements; Saint-Georges, Philippe ; Lenaerts, Cedric et alin 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 ▲] Detailed reference viewed: 10 (2 ULg)Non-Gaussian electrical fluctuations in a quasi-2d packing of metallic beadsVandewalle, Nicolas ; Lenaerts, Cedric ; Dorbolo, Stéphane 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 ▲] Detailed reference viewed: 8 (2 ULg)
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